When a e6300 is overclocked to the same speed as a e6600 (which has 4 megs of cache), it seems that the additional 2MB of cache doesn't make much of a difference. Also, C2D CPUs with 4MB of cache run hotter at the same clock speed.
The 4MB vs 2MB is roughly 7% advantage in performance, at same freqfency.
Also the 4MB C2D is not running hotter than 2MB C2D. The 2MB is actually an 4MB C2D with 2MB dissabled. There was an article about this, I'll try to dig it up.