My only concern is the quad cores. There are very few applications that use them. If this is gaming machine, i'd stick with dual cores. Another suggestion i would make would be get rid of the wireless keyboard and mouse. There's nothing worse than getting lag from your mouse and keyboard in the middle of a boss fight because the batteries are dying.
I've built my own rigs since i got my first Gateway P-90 when I went away to college. Ars Technica puts out a periodic
system guide that is a great start when building a system. With your budget I would look at the "Budget Box."