I can answer part of your question. Stepping just refers to the version of the IC you are getting. When the part first goes into production, it will be at some stepping (what stepping is determined by a LOT of things). As improvements are made to the design, the IC will be "stepped" which involves new litho masks and possibly other process changes to improve the die on the wafer. The die are usually stepped to improve end of line yield, but they are also stepped to improve performace as well. Sometimes, you get a stepping that REALLY works well and almost all of the die made with that stepping are very fast. Sometimes, you get enough really fast die that you end up not testing ALL of the die to it's full speed and end up selling die that COULD be sold as faster die as a slower part. This is always driven by marketing and market demand. But if you are the lucky customer that gets that 3.6Ghz part sold as a 2.6C, you are VERY happy. So, folks are always trying to find out what the latest "golden" stepping is and pick parts from it to try to get the really smokin part.
But understand, it is still a crap shoot. Even if you do buy a part on this new golden stepping, you might just get one that actually IS rated at it's true max speed and all your OCing attempts will be very much in vain. But if you get lucky...
I played that game back in the days of Covington (This was the very first Celeron. It was basically a PIII Core that did NOT have any of the L2 cache on it like the PIIIs did. Remember the Slot 1 Hershey bars?). When I decided to pick up my Celery, I called up a friend of mine in Sort and asked him how fast the normal PIII cores were testing out. When he told me that 90% were coming in over 500Mhz (remember, this was a time of 266Mhz Celerons and 400Mhz PIIIs), I jumped and picked one up. Did I get lucky? Well, that poor little Cerlery ran at 454 Mhz (on a 112Mhz bus vs. 66Mhz stock, faster than the best PIIIs at the time) for about 2 years. That thing absolutely SMOKED on Quake!
