I think you should just get the cheapest model from the line of processors you want. Regardless of what the processor is sold as, they all seem to hit the wall at the same speed of about 3.8GHz. The power consumption seems to ramp up really fast near the wall, so I think 3.6GHz is a more realistic expectation.
Phenom II X2 550 - $88 newegg ($44 per core)
Phenom II X3 720 - $104 newgg not including heatsink
Phenom II X4 925 - $129 newegg ($32 per core)
Phenom II X6 1055 - $200 newegg ($33 per core)
What's cool is that they can all hit that speed with the stock cooler. The 4 and 6 core come with a much better stock heatsink, so they will run at roughly the same temperature as the dual and triple cores.
I personally picked the X6, but I think the X4 925 is arguably the best value. Not many games will use more than 4 cores at this time.