Hey, i just went through that debate myself. In actuality the E6600 has a 4MB L2 on die cache which does give it a nice performance gain compared to the 2MB shared L2 cache you'll find on the E6400 and lower models. I've got an e6600 and my boss has an e6400, really outside of gaming you won't see any difference though as they are both really fast!
Byblyk.