Gah, all of these pre-builts are so unbalanced. Either they have an overkill processor (an i7 or a 2011 chip) and pathetic GPU's in Crossfire/SLI (HD7770, 550ti), or the complete reverse and pair a decent card with an FX-4100.
My advice is to build your own. It will come much cheaper, more powerful and greater upgradability than these builds.
Only one of these pre-builts I would suggest you get is this one. http://www.amazon.com/iBuyPower-Gamer-Extreme-AM987K-De...
Then put in your own graphics card and PSU. Though considering that the page itself cant decide whats in it (says an i7 in the picture despite the spec sheet saying an i5-3570k, no HD7750 in the sheet yet claims it a bit further down). I would just build a machine yourself.