All of the Penryn chips use these steppings (C0 or E0). The difference is overclockability. I don't know if there are multiple fabs that make them, but my E0 Q9550 came from Malaysia. It said so right on the chip, and I had read somewhere that the C0 came from elsewhere?
Bottom line: E0 is the better way to go.
i have a penryn and it is a M0 and it is at 4.0 ghz atm, with 1.3 volts.