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).