Tried to edit, but didn't let me post, so here:
EDIT: Oh, and few days ago, I was reading legionhardware.com, they made just 900$ config WITH monitor/speakers/keyboard/mouse (no windows), and it's still almost as fast as your "low" configuration, as it uses same HD3870, and only huge difference is C2D 4500 vs your quad Athlon. But it's WAY cheaper, as you DO GET EVERYTHING for 910$!
And oh, EVERYONE likes to go out and put 600-700-800W power supplies in their "building-a-pc-review", and every time they bench something they confirm that "whole system" runs under 300 for similar hardware.. let's give it 20% of wasted energy, it's still no more than 400W power supply needed, 450W if you want to be sure its all fine and dandy.. So why on earth if (for example) C2D E6700+8800GTX XXX edition+raptor+DVDRW spend 300W as a WHOLE SYSTEM (google it! try it!) does every single reviewer offer us 600+W power supply. You did the same with both "low" config (600W? for what? 55nm GPU and an athlon quad?) and this so-called "midium" one (750W? LOL! Even 550W is more than enough here, even with GTX and Quad CPU, and even if you overclock like hell you won't waste double the power than). Your own Skulltrail review measures 2x quads with 8800GTX OVERCLOCKED TO 4GHZ (!!) to draw 630W. So you can probably power well overclocked Skulltrail system with this 750W power supply.. So again to the start - why using 600+W power on low-mid configs with SINGLE CPU, and SINGLE GPU?