I'd probably look to spend 1k at most on the computer (more for the keyboard/monitor/mouse). Building your own PC isn't hard but it helps if you have a friend that has experience with it. Look for ~6-8 gigs or ram, don't go for dual GPU's just stick with 1 decent one. Processors are weird, i7's are the best, the i5's, then…
Very nice spec, pretty much the same as mine except I got the GTX275 since the DX11's weren't out (ahem not that I could afford one anyway :D ). Should rocket through anything you throw at it. Have you looked in device manager and smiled at seeing 8 processors show up? Always a nice feeling! Nice build too, cable…
I'm sure 6 would be good, i've got 8 in my system now and its plenty for of 99% of tasks, but the next time i buy a new pc, i'll get 12. I dont know how thoroughly you tested there, but try leaving those apps open for a few hours and actually working in them, i bet you'll notice some memory issues then! =D The ideal…