If I am remembering correctly, the difference is:
1. A ~%5 shrink, when they went from cB0 to cC0.
2. A few new bug fixes.
3. A few new bugs causing difficulties at high speeds (including one that caused Intel to recall tons of 1GHz+ cC0 chips).
4. cC0s overclock a little bit better, but as always, you can get a dud cC0 chip that will do a LOT less than the average cB0.
Nack