Okay, I didn't get any information here, but I got some replies over in another forum.
Anyway, I'll just update everyone here.
The B2 stepping is Conroe, while L2 is Allendale. The B2 does overclock better than the L2. Someone with both E6300s has reported an overclock of about 3.3ghz on the B2, while the L2 almost reached 3.0ghz (even after massive overvolting). This is on the same system, with CPU swapped over. L2 overclock was checked a few times (includes re-seating).
This is not to say the L2 isn't good, but the B2 is definately better if you're after a good overclock.
Also, just as extra info, lookout for "B" weeks of any CPU: they seem to overclock a little better, but the Conroe core gives a much bigger advantage.
ie: B2 stepping A chip is better than L2 stepping B chip for the E6300.
Also, to check for Conroe/Allendale, apparently Conroe's Batch# starts with L6, while Allendale's starts with Q6.