All E6600s are B2 rev cores, the only difference is in the FPO batch number. There are A, B, F and G batches; for instance L628A, L628B....ect. There is a general pecking order of them too:
B = higher temps, lower (compared to A) voltages but usually a fantastic overclocker
A = lower temps moderately higher voltage, but also generally lower overclock compared to B, but are still very good
F = higher voltage needed, higher temps mediocre overclocker at best
G = high voltages, high temps, and is generally regarded as the poorest batch