Opteron's suck at gaming, even dual-cores. The clock speeds won't just add up on each other. The two processors just supplement each other to be more efficient in applications like Maya, Photoshop etc. You've got lots of RAM (too much if you ask me...), but registered RAM is slow. It's stable and therefore good for servers, but it loses in speed.
The two 7800 GTX's will be great for gaming (although I'd rather wait for the X1800 XT to come out
). I like the monitors...very nice.
PC Power & Cooling makes the best PSU's in the market, but the 850w is just overkill. That system won't even use half of that power, so why waste $400-$500 for it? Too much hard drive space too...just get 2 of them and you'll have TONS of space for less money (better yet, just wait for Hitachi to come out with their 1TB desktop hard drives
I've heard some mixed reviews about those Plextor SATA drives...some say they work fine and some say that the quality sucks so much that it won't even read commercially stamped disks.
The Creative SB X-Fi is the best, but it's not practical considering the price. Just stick with a Audigy 2 ZS Platinum or Audigy 4 Platinum and be happy (you won't notice much difference anyways).
The Logitech MX518 is great. I love it. I'm using it right now and it's just awesome. Although I'd rather have the Logitech G5 or the Razer Copperhead (2000 dpi baby!).
Quick summary of your "Ultimate" computer:
It has good parts but is impractical considering the price. And if you're going to use this for gaming, you're wasting your money. Heck, even for a workstation/server, this is a waste of money.