alot, ive had the 2, with b3 i got temps over 80c with stock cooler on prime 95, it cut it off at 80c with g0 and stock cooler it was like 65 max i dont go over 45 now with my g0 and tuniq tower 120
It means exactly that, just different manufacturing processors..
People often times confuse the two.
But it is for the newer models:
Stepping: B
Revision: G0