For those that do not know the boat it is very similar to the Formula 280SS, It has twin Mercruiser 5.0MPI's (260HP), alpha drives (1.62) Mirage plus 19s, I am hitting the overrev alarm with a light-medium load, is it best to work the 19s or go to 21s and then work if needed? I would love some more up top and good cruise speed, it comes out of the hole very good with the 19s on it currently.

If you are hitting the rev limiter/alarm with 19s then I would step up to 21 inch pitch.

I would get a set of 21's and then decide which set to primarily use and/or modify.
Keep the other set as spares.

I've been looking for a set of 21s to try, just didn't know if I would gain anything from working the 19s versus going to 21s