Back when I did enduros, I compared a loop on my daughter's 200xcw vs my 250exc. I was faster on the 200. Some of that was slightly different gearing, some was that it was a little easier to ride. There is a couple of pretty fast guys in D23 that used to ride 300s that now ride 200s. They say they take less energy to ride fast, plus it is easier to ride a 200 wide open than a 300.
all around good guy