That comp is not a bad deal for 100 dollars. As for the CPU options if the Mobo that it has in it can only support up to the 4800+ as we speak check the website for the company that makes the mobo and see if they have any recent bios updates that will allow you to put a better processor in that you looking at (5200+). Usually they may have something that will help you update it but unless you are skilled with computer work and know how to update a bios I would not recommend updating that yourself. If it is done wrong it will fry the mobo and make it unusable so if your not sure how take it to a professional to do it they will usually charge about 50 dollars to update it.

As for the cards Im running some older cards in mine the 512mb Nvidia 8600 GT OC2 with thermocooling from BFG in sli at the moment and I run 3 boxes just fine with about 45 FPS in reg PVE area, about 25 in PVP battlegrounds and about 16 in dalaran at the moment (as we all know dal is pretty nasty on the FPS lol) so if you want to get the good FPS you can go with that or better yet try the 9000 series from Nvidia the prices on those things have dropped majorly since the 260 and up have been released hope this helps if you have any questions just repost and ill reply shortly.