Generally, as newer steppings come out, higher speeds are reached in both stock and overclocked setups. The C1 got a ~ 10% die shrink from the B0. All the C1 CPU speeds grades come off the same wafer. Intel makes a wafer with (I dont know how many, but a lot...200??) of CPU's on it. It is sliced up into individual CPU's. They are tested and binned. the ones that pass the test for 2.8 get locked in at the speed. Lesser chips get a lower speed grade. But guess what? The yields are so good that most will pass the higher speed grade. If there is a demand for lower clocked speeds such as 2.4, 2.0, etc they will be locked in at and sold at that speed even though they pass the test for higher speeds. The C1 stepping came out for the 2.66 and 2.8 CPU's. That means you have a good chance of hitting those or above speeds when you buy a lower clocked CPU with a C1 stepping.