PG278Q has 144Hz refresh, PG278QR has 165Hz refresh. Refresh rate = number of times the display is drawn/redrawn per second = maximum possible fps that can be displayed (without G-Sync throttling fps down to reduce tearing and stutter, lol).
Ask how many games do you actually play at 144fps? And would 165fps make these games any better?
Some reviewers (and all salesmen) claim that they can immediately see the "huge" difference between 165Hz vs 144Hz by eye. I never saw any difference, neither did any of my hardcore nerd buddies, even while balancing various quality settings on games pushed from 150fps to 200fps.

At 144Hz a display needs to draw/redraw those frames (or even single pixels) in slightly less than 7ms, at 165Hz in slightly more than 6ms. So <1ms response time is really quite overkill, <5ms is more than enough.

These two Swifts are otherwise nearly identical.
PG278Q uses (discontinued) AUO M270Q002 V0 TN panel, PG279Q uses AUO M270Q008 V0 AHVA panel, PG278QR uses a "newer" AUO TN panel (rated at 165Hz refresh).
PG278Q overclocks the NVIDIA G-Sync "1.2" Module from 120Hz to 144Hz. PG278QR overclocks the NVIDIA G-Sync "1.2a" Module from 144Hz to 165Hz.
Both models can display 24-bit (>16.77M) colour depth, although sRGB spec on the PG278QR 100% vs PG278Q 93.9%.
Both models have 1000:1 Static Contrast but Dynamic Contrast on the PG278Q is 1000000000:1 while the PG278QR is merely 20000000:1.

sRGB is a colour standard - so colours used on displays, cameras, printers, software, games, and internet are reproduced accurately (to the human eye). 93.9% sRGB means only 93.9% of the RGB colour space (visible colour spectrum) has exact fidelity, in practice it's usually the extremely dark (blackish) RGB tints which are inaccurate enough to fall out of sRGB compliance.

Contrast ratio is a measure between the brightest (whitest) and the dimmest (blackest) pixels on screen. Static contrast is what you see on stillframe images (photos). Dynamic contrast is what you see on multiframe images (videos, games). Dynamic contrast ratios are largely improved through codecs and software manipulations, higher ratios can make videos/games look better but aren't as meaningful as their huge values imply.

Debate over the merits of TN-vs-IPS never ends. All I can say is that I think descriptions of "washed out" colour/clarity on TN are much overhyped: premium TN displays produce excellently rich and vibrant colours, IPS does indeed look a little better but it's really only noticeable in a direct side-by-side visual comparison. Swift monitors aren't about *colours* anyhow, elite professionals would never do film or photo work on a Swift, lol. Swift monitors are about *motion* and about displaying things in motion as smoothly and flawlessly as possible, allowing for immersive experience through uninterrupted (game) flow.

PG278QR of course comes with the latest-and-greatest OSD/firmware which includes a larger suite of features, programs, and toys (er, "ROG Gaming Technologies"). If you make good use of these things then the new Swift likely includes features and add-ons and improvements you just won't want to live without. If (like me) you basically never use any of them at all (except experimentally) then the new Swift likely provides a bigger pile of tech toys you'll basically continue to never use.

I don't think upgrading PG278Q to PG278QR is worth the cost. I think upgrading PG278Q to PG27UQ would be far smarter.

I'd also wait until the current scandals about "G-Sync DRM" and "chipless/software G-Sync emulation" play out. If things go badly for NVIDIA then G-Sync take a significantly price hit (to reach parity with FreeSync) ... or it might suddenly become a defunct proprietary standard. It's also worth waiting for details on upcoming AMD GPU offerings - they've lagged for years and but now they're back in the game - it might even turn out that you want a FreeSync monitor more than a G-Sync monitor, lol.

I think the PG278QR was released because there was no 3D Vision monitor with a HDMI port that could be used with a console. The older PG278Q only had DisplayPort. If you don't care about 3D Vision, then get the PG279Q. I don't see any reason for ASUS to release a new PG279QR since the existing model has HDMI.

The best current and upcoming models are:
PG258Q - 3D Vision 1080p 240 Hz
PG278QR - 3D Vision WQHD 165 Hz
PG279Q - IPS WQHD 165 Hz
PG35VQ - HDR Ultra-WQHD 200 Hz
PG27UQ - HDR 4K 144 Hz

I personally have a PG278Q and a PG258Q. I bought the PG258Q for HDMI and 240 Hz However I found the smaller PG258Q to be significantly less immersive than a 27" screen, so I'm selling both and buying a PG278QR since both HDMI and 3D Vision are important to me. I'll hold off on HDR and 4K until I do a full system upgrade.

Few games support HDR. Shadow Warrior 2, Mass Effect: Andromeda, Hitman, Resident Evil 7, Obduction, maybe Rise of the Tomb Raider and a few others. Unreal Engine 4.15+ implements (experimental/beta) HDR, so a whole pile of UE4-based games might be updated to support HDR.

Not that simply bolting on HDR support automatically means HDR awesomeness. There's a certain amount of artistry involved, some games (whether they be "photorealistic" or "animated" or whatever) just don't have the sorts of artwork or graphic style or visual components which would look any better when seen with HDR. I expect to see many game titles proudly advertise themselves as "HDR Ready!", just leaning on a new technical feature in the engine, without actually putting any work into fully/properly crafting their graphics or effects to look great with HDR. It turns out that most games have dark, closed, limited environments and somewhat less complexity in terms of reflective or glass/metal surfaces (so the GPU load can be shifted elsewhere) - and these are the sorts of things which wouldn't really look better with HDR anyways.

I admit I haven't played games on HDR monitors. Maybe the difference is (or will be) more profound than I expect.

I have watched TV and movies on HDR TVs. And I've noticed the difference is not qualitatively obvious, it's more a sort of subtle overall impression. Only noticeable at all when it's exceptionally well done or when you're specifically looking for it. The vast majority of content (movies, TV series, etc) that I've seen on Youtube/Netflix/Exodus and on DVD and Blu-Ray discs isn't actually filmed to HDR standard anyhow (and there are, in fact, four different HDR standards - HDR10, Dolby Vision, Technicolor AHDR, and HLG - each with slightly differing technical merits, advantages, and tradeoffs). Large cinematic panoramas and open environments populated by objects at all depths of field can look great with HDR, high range of contrast (and thus High Dynamic Range of contrast) in lightings and shadows and tints ... while scenes with weak or sporadically uneven lighting or vivid colours or layered shadows or tons of smoke and fog ( games) tend to actually look worse. More and more programming will use HDR in coming years (maybe even "HDR remastered" versions of all my existing movie files and discs?), but for now it's basically unused and inert (even counterproductive to quality) most of the time.

I'm sure other opinions might differ. :rolleyes:

4K resolution is definitely worth it, you'd never want to go back to anything less. G-Sync or FreeSync is a love-it or hate-it or meh thing, different for everyone but expensive for all. I would never prefer HDMI over DisplayPort for main display, although it's always useful to have one or two HDMI ports for plugging into stuff like that Android box or a DVD/BR disc player.

I really need one monitor that does it all. I have gone dual-monitor twice and regretted it both times. Your head is always at an awkward angle when gaming, and for movies the centre channel dialog does not line up with the monitor. The PG278QR is the only model that satisfies all my requirements:
2560x1440 - This is the only feasible resolution to game at. Not even GTX 1080 Ti SLI can run 4K reliably and neither will a GTX 2080. Upscaling looks blurry and unacceptable on every monitor I've seen. Maybe a 4K or 5K screen with true nearest neighbour pixel doubling will resolve this.
3D Vision - I watch 3D movies a lot and 3D Vision is simply the sharpest, most realistic 3D implementation I've seen, apart from the Oculus Rift. 3D is not a gimmick - Low quality TVs and theatres are.
G-SYNC - It's required at 2560x1440 since it makes even 40 fps playable.
HDMI - I need this for consoles, since I don't have a TV. My desktop PC is my primary "home theatre".

As for HDR, I suspect it will be like Dolby Atmos. I just bought a Dolby Atmos system for my PC. At first I could barely hear any improvement and thought it was a waste of money. But when I switch off Atmos / Dolby Surround, the whole sound stage collapses into a flat plane and sounds non-immersive in comparison. I can't imagine going back to a non-Atmos system, even though most content is just upmixed. It's the first upmixer that isn't a gimmick that sounds worse than the original content.

I may give up 3D Vision and buy a PG27UQ when it releases if 4K is playable and applications finally fix their DPI scaling issues. It's also unknown if HDR will work over the HDMI port for consoles.