Last time to LC, I ran a 23P Rev 4 prop... this is by far the best all around prop I've run so far.
Runs decent #s and handles great- espically in the rough (guessing because I'm not trimmed up as much) Flies great and lands level. Maybe lost a mph or two, but its well worth it. I saw 75gps with it which I figure is not terrible for a first run loaded up for an overnight and still figuing out where it likes the trim set.
I went from a 25M+ to the 23P Rev 4 because I've read that the Rev 4s acted like a bigger prop than the M+. Worked out good.. maybe gained 100-200rpm, if that. Paid more attention to how it was handling than rpms. 50mph is around 3800-3850rpm.. so at 50mph cruise right around 10% slip.. little more than the M+.
It felt really weird at first.. the boat is pretty much level at speed... just feels really different with the overall lifting prop vs a bow lifter. Takes some getting used to..
Wonder how it'd do on the 21? Pitch is way too small, but it'll work for testing purposes.