Hi,
ignore synthetic benchmarks (esp, all in sequential readings used to market these drives. 1800MB/s my ass)
I have numerous different SSDs here, ranging from 512GB 840Pro/850Evo in workstations and 4 TB (4x 1TB 840EVO ) in fileserver (plus few times that in conventional HDDs)
I also tested at home single NMVe drive recently (it doesn't matter if it's m.2 or PCI Express, I know that you know but I had a look at ChaosGroup forums and people think even regular SSDs in m.2 are faster...I cannot help myself there....),
namely 400GB Intel 750, which is either as fast as SM951 or roughly equal counterpart based on available benchmarks. Mark that these drives area already much better in performance than any Raid setup (or internally raided SSDs like Revo).
Real-life results ? Bootup and app starting times are slightly....slower. Expected since it's consistent with benchmarks. Sequential writting is massive...but we're not doing that in workstation. I am only starting PC (one a month), 3dsMax and Photoshop.
Now this is 400GB (equal to 512 SM951). You're looking to buy only the 256GB SM951 which is worse.
My takeaway is it's not worth at all, or even good as system drive. In my most recent workstation, I didn't even bother with 850Pro, and went with 850Evo directly because I could buy 500GB cheaper (installed in 8.1 with 64GB memory swap it's only meager 380GB available).
Regarding Raid 0 Setup of SSDs. Just shortly no. You won't improve anything at all past sequential reading, and scene data aren't large enough to benefit at all either. It's wasted money and potential risk for data safety due to stripping.
And what sort of project data are we talking that you would only need 256-512GB in Total capacity ?
If you want speed, buy 840/850 Evo 1TB, if that's enough for you. It costs just as much as your above scenario but gives you twice or quad capacity.
TL,DR:
There is no magical new technology in storage hardware for workstation purposes. Single layered SSDs are not 'old technology'. Raid0 is still stupid in 2015 as it was in 1995. But twice so with SSDs. 256 is not enough for system disk anymore, 512GB is definitely not enough for storage. Invest money where benefits are reaped (capacity), not snake oil (synthetic numbers).