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Is it truly conceivable that you'll use anything like 32 GB RAM? I ask because 16 GB is incredibly generous and hard to saturate. Since the rest of your rig is targeted for cutting edge performance with today's tech, I would consider investing in robust 2 x 8 GB 2133 sticks which would take some overclock load, either to try and bump their MHz up or their timings down. Combined with your RAID 0 endeavor and pushing the CPU, this might be worth considering if you really want to dance on the top performance edge, especially if the CPU can go even to 4.5 GHz.
If you find yourself short on RAM, you can add in another 2 x 8 GB down the road a bit. Prices will only drop.
Agreed that 850 W for PSU is substantial. I would be interested in seeing how much load you actually put on it once you ramp up the clock a bit. My suspicion is you'll be comfortably under 700 W unril/unless you add the second GPU.
I think that you will not be able to find a matching GPU in 2 years. the tech will advance too far and you'll have to buy two new ones at that time. Might even have to upgrade PSU then ... but I also think power use will improve by then too. So, who knows.
The price range you're in, I don't see you being concerned too much about shaving $50 or so off, so dropping the PSU to 720 or 750 W probably isn't worth the effort, apart from the fact that if you are using too little of it's capacity (under ~60% I think?) then it's efficiency falls off pretty dramatically.
Overall, I don't see any major issues. The above is more like musings. Personally, I'm not sure I trust 3 TB tech yet. If money really isn't much of an issue for you, consider 2 x 2 TB Western Digital Caviar Black for greater reliability. You can always change those out in a year ... just fill 'em with archival material, shelve them and replace with the most reliable 3 or 4 TB models available for late 2013 or early 2014.
