C0 stepping for QX9650 and QX9775, same processors, different packaging (QX9770 LGA 771), the QX9775 is the highest binned processor for the C0 stepping.
C1 stepping for QX9770, minor manufacturing update to C0 stepping. AFAIK the C1 stepping is the process used for Xeon Quad Core processors with 333MHz FSB.
However I think the C1 stepping will not overclock as well as the C0 stepping because the C1 stepping has a lower thermal specification.
AFAIK if it has a lower thermal specification then it should overclock better because that means it pulls less power and creates less heat at the same clock speed.
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John H.
Testing/OC Team
@iBuyPower.com Custom Built Pc's