I use the most budget quad core in the phenom range which technically is an athlon. That is a 3.2ghz 840 x4 quad. I use it at stock with a gtx 560 ti stock and really i can play any game there is more or less at max, skyrim at complete max, cyrsis 2 maxed at very very nice rates.
So yes a phenom II will do the job just fine, however if i were you i would get an i5 just because it will last you a fair while longer. Whilst my budget cpu does the job just fine, i can see where a more powerful cpu would be advantageous, especially in online games where the influx of information can at times make my FPS slip awfully close to 60FPS which can ruin the fluidity if it ever goes beneath that mark, which it rarely does but still. A year on i do not regret buying this cpu at all for 100 dollars, but at this point in time i would dish out for the i5 so i wouldn't have to worry about upgrading for a while.
If you are on a tight budget though, get a decent phenom ii black edition so u can OC that thing if you really need to which will prolong its life, and don't spend much time on thinking what if because it will do the job. It all comes down to your budget.