Okie.
The clawhammer has 512 MB L2 Cache. It runs hot, and is not originally a socket 939 CPU. Not recommended.
The Venice is better. Has 512 Mb L2 Cache, rut slightly cooler than teh Clayhammer. Recommended.
The San Diego is so far the best for Single Core CPU. Has 1 Mb Cache, and is used for high-end AMD CPUs.
If u only buy a CPU for gaming, then i would suggest any San Diego Single core CPU. If within ur budget, then prob u could go for a dual core (4400+ best ) or a opteron 170.