Just for clarification, they aren't really processors, they're cores found in processors, which come in a number of clock speed variations.
San Diego has double the L2 cache of the Venice at 1MB. Cache size has a relatively small effect on performance so it's not a very big deal. I'm personally buying a San Diego just because it's not much more expensive than the same processor using Venice and I'm quite certain that 512KB cache will start to cut off (excluding Celeron/Sempron).
Intel C2D E6320 / AMD Athlon X2 3800+
Gigabyte 965P DS3 / DFI nF4 Ultra-D
2GB OCZ Gold PC2-6400 / 2GB OCZ Gold PC4000
eVGA 8800GTS 320MB / eVGA 6800GS 256MB
150GB Raptor / 74GB Raptor
2x500GB / 320GB
OCZ GameXStreme 850w / OCZ StealthXStream 600w