I'm thinking in totally the opposite direction. I say you set the rpm and then don't change it. Let the boat speed vary. To qualify as an official towboat it has to be able to run a pass with a sled to a specific tolerance w/ the RPM fixed. That is the baseline, everyone has to deal w/ it. Lighter skiers would get faster end of tolerance times and bigger skiers would get slower end times. No processors, algorithms, reaction times to deal with. KISS. If you wanted to make it a bit more complicated (and arguably fair) then have several sled weight baselines that a skier would have to use based on his/her weight. Don't most other sports have fixed equipment to deal with?