X2 5000+ Black Edition all the way. Current Phenoms don't perform well in games, and they often get outperformed by their X2 counterparts.
X2 6000+ is also a good CPU, running at 3.0Ghz. However, since its 90nm based, chances are it will dissipate more heat and consume more power than its 65nm variants.
On the other hand, X2 5000 BE is a dual core 2.6Ghz CPU, based on 65nm process node, with unlocked multiplier. Chances are you can overclock it to 3.2~3.4Ghz with absolutely no voltage increase at all. You won't risk damaging the CPU as well.
Here's Tom's article on overclocking 5000+ BE.
http://www.tomshardware.com/2007/10/22/budget_overclocker/