I think you'll find that with computer components, much like anything else, there is a lot of opinion mixed in with the facts. So, having said that, here's my feedback:

System looks pretty good overall. I agree with the PSU upgrade.

As far as the video, I can tell you that right now I'm running a gtx260 on a 30" monitor and I'm not satisfied with the Northrend performance. However, I am sure that my (greatest) bottleneck is CPU (Core Duo), so I'm building myself an i7 machine as well. My feeling is that once I do, a single gtx 260 will be sufficient. However, they are currently running about $240 so I just decided to go ahead and get another one. No reason to build a BA machine and then hobble it for that kind of money

BTW, I believe that WoW will use SLI just fine. Where it gets tricky is if you want to use multiple monitors (I do). Currently, X-fire works over multiple monitors and SLI doesn't, but Nvidia is planning to fix that RSN as I understand. I think where a lot of this "wow doesn't make use of SLI" comes from is that wow isn't a very GPU intensive game so something like SLI is usually overkill, but that's not necessarily true when you are running multiple clients at these types of resolutions.

My advice: Get your computer and see how it runs. If it's not good enough, get another 260 and SLI them and see how that goes.

Regarding the hard disk: I don't recommend RAID for two primary reasons. 1) most of the commodity m/b raid controllers are not hardware solutions meaning they will not perform nearly as well as you might think AND they are using you CPU more than a non-raid configuration. 2) The little performance increase I noticed on the last two I tried was not worth the fact that if either disk fails or the RAID parameters get reset you lose all data. It's not like other types of failures where you might be able to stick the drive in another computer as a slave and recover the information. When RAID0 goes bad it goes really bad.

FWIW, I have found the best multibox wow setup to be an SSD with the WoW Data directory (don't need the other directories - there isn't that much there and SSD drives aren't swift on writes so you don't want changing configuration data and such on it) that is symlinked into multiple wow folders as needed, all on the same drive - this is currently how I have mine setup. If you're interested in why, there are quite a few threads around here about it, but that's been the best configuration I've found.

Good luck, and enjoy the new computer.