I would change the video card to a 4870 and $30 - $60 there without losing performance. You could also go with a single 1tb drive and save $50. You really don't need a 850W Corsair, the $100 750W model would still be more than enough for future crossfire.
Well, RAID 0 is less reliable (2x) just by the way it is done, but as long as you back up regularly (or just have unimportant stuff: games) then it shouldn't be a big issue. I'm doing that for my i5 rig.
You probably could get away with the 750 from Corsair, but as the prices on both of them are good and close right now, I don't see any reason not to get the 850.