The best chipset, best in every way, which can run AM3+ is 990FX+SB950.

There's less than a dozen mobos with AM3+ and 990FX+SB950. The Asus ROG Crosshair V Formula-Z is the very best one of these. There is only one competing motherboard with only one slightly better specification (supports up to DDR3-2450), and it costs less, but it has a lot of other tradeoffs and limitations.

In practice, max supported DDR3 speeds will depend more on your processor than on your motherboard.

thanks, yes I was either thinking of going with the crosshair formula z or the asrock 990fx extreme 9 but judging by the two responses I'll think I'll go with the crosshair now would the fx8350 be a could match for this mobo also is a 850w corsair psu good enough for sli

I'm not sure if I'm doing this right do I just post a question and wait for someone to respond is it

The FX-8350 has one integrated dual-channel memory controller which natively supports up to DDR3-1866.

The quality and capabilities of the iMC vary from part to part, some CPUs will be able to support faster memory, a few will even be epic, others will not. AMD rates this CPU for DDR3-1866 (if not then it's a defect and can be replaced under warranty), but there's never any guarantee about thresholds when overclocking. Some online searches show that most overclockers report using DDR3-2133 or DDR3-2400 offers best results. The CVFZ fares a little better than most of its competitors, but even so it achieves DDR3-2400+ only when paired with an "above-average" processor part.

So don't get anything slower than DDR3-1866. And don't waste your money getting anything faster than DDR3-2400 (fastest OC officially supported/expected on your mobo). Because of the way the dual-channel memory controller is hardwired you probably won't see any real difference between a 4x4GB kit and a 2x8GB kit, nor much real difference between Single-Sided and Double-Sided DIMMs.

This G.Skill 2x8GB DDR3-2133-9-11-11 1.6V kit seems like a good deal at £58, better than the DDR3-1866 kits which cost about £55, and the next step up is DDR3-2400 which starts around £70. The G.Skill, HyperX, and Crucial DDR3 products look reasonably priced; the Corsair, Mushkin, and GeIL DDR3 products look overpriced; I'm not really familiar with other DDR3 brands, and I'm not sure if those prices from one vendor are really representative of prices in your area. You might choose to pay a little more if you're particular about brand or colour/style, etc.

You might require a little extra cooling for your RAM. I personally think adding/upgrading fans to increase chassis airflow is generally a better approach than spot-cooling with RAM Cooler accessories, but opinions and styles and results do differ.

ram, 1866 - 2133mhz range.

https://www.asus.com/ROG-Republic-Of-Gamers/CROSSHAIR_V_FORMULAZ/specifications/

just be shure to have a good CPU cooler and remember the ram height when choosing cooler.

get one kit of ram and dont mix kit's if you buy several to got the amount you want.
even amd is more forgiven when it comes to mixing ram i would not do it.
if you are going 8gig, get 1 stick
16gig go 2x 8gig sticks
32gig get 4x 8gig ones

look on the memory maker's homepage and see if they have memory calculator so you can see what memory is supported on the motherboard you are going to buy.

her's gskill's ram configurator.
http://www.gskill.com/en/configurator