The fulls size desktop would offer better performance as you would not be limited by uATX boards or cooling limitations. So I would recommend you go with the full tower case if you can.
Anything more than DDR3 1333 isn't needed for an i7 platform. Even 1066 is hardly any slower than 1600 as i7 just doesn't seem to need the extra bandwidth at this time, same for Phenom II.
So just save your money: http://www.newegg.com/Product/Produc...82E16820220367
I would go with the HD 4850 X2
. I've only just noticed it at this price and it beats the GTX 275 in almost every benchmark.
Here's a modular version of that PSU for the same price.
The Xigmatek PSUs and the Corsair VX line have the same OEM, Channel Well.
The 900 used to be available at a good price, but it seems to have risen again. I would recommend the CM RC-690
, it's a bit bigger than the 900 as well.
If you really want to put that much money into this, scratch the lanbox and get an intel i7 965(thats the extreme), and get the GTX 295. Also get a cpu cooler. The coolermaster v8 looks BEAST. Also if you want you can buy the corsair tx850, i know its 100 more watts than the corsair u listed but its only like $20 more, if you want.
The 965 is 4 times the price of the 920, it uses the exact same architecture. If someone is considering the 965, they need to be an experienced overclocker, and they need to have money to burn.
He only need an aftermarket cooler if he's overclocking, which it doesn't seem he is.