ohhh... less than $30 sounds good... I'll wait for that... just realized that the 3.1 card probably takes that last PCI slot anyways... so m2 is probably the way to go...

Due to the placement of the M.2 socket on the R5E, using the ASUS Hyper Kit might obstruct the GPU in the first PCIe lane.

Another option would be to use a PCIe SSD card instead of an M.2+PCIe. These are typically a striped RAID array of 2-4 discrete SSD controllers and NVRAM modules (plus some amount of DRAM cache) embedded onto a single card, all seen by the operating system as a single indivisible drive/controller.

The ROG RAIDR, Plextor M6e, and G.Skill Phoenix Blade all offer impressive Read/Write/Access (similar to SATA SSDs in striped RAID configurations). Some models are available with prices, capacities, and performances comparable to (or much better than) the Intel 750. And they don't occupy any PCIe 3.0 lanes or utilize a dedicated M.2 slot (which means they also don't lock out any other slots, ports, or other hardware resources on the motherboard). You could conceivably populate a motherboard with many such cards and move them from machine to machine with little difficulty.

These cards have been used in enterprise-class machinery for a while, and are now a "mature" storage technology which offers greater speed, reliability, longevity, and flexibility than consumer M.2 storage. I honestly don't know why M.2 is being pushed hard into the mainstream while PCIe SSDs are still seen as an oddball "niche" item (but I suspect most consumers think M.2 is the best new thing out there because they see every new motherboard proudly advertising M.2 compatibility).

Incidentally, a striped RAID of 2 or more good old SATA SSDs will offer similar (superior to most M.2) performance and price, in my opinion. It's hard to beat the price and performance of a striped pair of Samsung 850PRO SSDs, doubly so when their performance is multiplied through their RAM-caching software.

You may be right. It doesn't hurt to look at the shocking numbers on the benchmarks, lol. The Intel 750 M.2 is fairly respectable, but I feel there's a lot of better options.

Regardless, if available space/geometry is constrained then you may still need to defer the M.2 solution. I don't think any 12GB Titan X cards are going to come out in small (<9") form factors, lol.

[Edit]
Far be it for me to criticize Asus (especially on their own forums, lol), and to be honest, I have been entirely pleased with my excellent RVE mobo (so far). But it seems to me that since M.2 is still an evolving nonstandard addon, and since using it typically imposes tradeoffs on other (finite) mobo hardware resources/space, it would make sense to physically position the M.2 in such a way that populating it with a full-sized module interferes only with the particular slots/ports it happens to lock out. Just sayin'

OK... question.... is there a difference in performance between the 750 PCI and the 750 in m2?

Theoretically no, I don't know anyone with the 2.5 inch drive though, there will always be trade offs especially running multiple GPU's, you have to give up something, in your case either the Intel 750 or the USB 3.1 daughter card. The Samsung SM951 is a very fast M.2 drive and in the coming months we will see new drives being released