Moe, and anyone else reading this, the 2100 thin ring piston is not "magic". I would say it gives about the same increase in power as a low restriction air filter. It does not give as much as a muffler modification on most saws. The amount of power increase is appreciated in race saws because everything helps. Another way to say this is; If you took two new 2100s and broke them in, the thin ring model would be faster (this is a general statement not taking into account differences in production tolerances etc.). If we then do a minor modification (one known to produce additional power) to the thick ring saw, It now becomes faster.
The thin ring saws best attribute was the low tension applied to the cylinder walls. This is where the additional power comes from. There is less parasitic loss. The woods guys liked the thin ring because about once a season they could stick in new rings and the saw was good to go again. With the low tension, there was hardly any wear on the cylinder plating. The rings wore out fast, so the cylinder didn't suffer. Point is the thin rings for the 2100 are no longer available so it becomes a moot point. My opinion only here but I think if two guys went to work for a day in the woods and one had a 2100 thin ring and one a 066 Stihl that the production would be about the same. The guy with the 2100 is carrying more weight though. The trees were generally bigger during the 2100 heyday. Had the 066 been around at the same time, I doubt many 2100s would have been sold (if price was comparable). Mike