Gill,
We had 130 kgs crew wieght on the f18 so we had to sail small rig. IMO it does a pretty good job of evening things out. We found we could climb slightly higher than the other boats upwind but not as fast. Reckon it worked out to be about even in that direction. Downwind about the same as well. Unable to match the speed of the heavier crews when sailing hot tho.
Definetly makes the boat easier to control for a lighter crew and it did get quite windy in the last race.