its differs for every the proc models...

like e8 series is said to have better OCing ability with E0 stepping compared to C0...

while q6600 is said to be better OC n running cooler on G0 compared to B3....

for those comparison, it doesnt mean that C0 cannot clock better than E0.... most of the time its down to the ability of the proc itself imho.... just that getting the better stepping increases ur chance of getting a more OCable proc...

my 2cents...