I'll take advice on the CPU, but I really don't see the need for a quad core, almost everywhere that has debates on this pretty much just say it's for longevity, and I don't see the need for extra cores right now or in the next year or two, if you know different then by all means please post about this.
Basically this is a machine built for 25 man raids on WoW and to play L4D2, and maybe the new Star Wars mmo coming out next year.
the Tom's article lists the Athlon II X3 as the best budget chips right now. They have enough power and overclockability to play any game and even though most games now still only run on 2 threads still it leaves you one open for if your virus scan kicks on or the like.
Finally the only other piece of advice I have is get a larger psu. They run at their most efficient around 50% load so it's better to aim a bit high. Will help on your power bills and on the longevity and upgradability of the computer.