I remember an old post of Andy Daff who had done some serious Vmax with an Acid 74, but I cannot find it anymore, sorry...
The problem of using race sails on a wave board is the amount of power you can push over the thin tail and small fin. With wavy rails on the tail and a inboard/centered rear footstrap, there is very little to push against.
Sometimes, I'm using my seat harness with the wave board to really blast around. I have better power with the legs in overpowered conditions and it's easier to go upwind in a locked-in attitude. However, it's also easier to get serious spinout if loading too much the rear foot on a deep reach (easily done with a seat harness).
I guess this might be more efficient on the tail block of the Kombat 79 with outboard straps and a tad thicker rails than that of the PA 74 (no problem with a RS1 6.6 sail on my Kombat 86 and the stock 30 cm freeride fin; but the tail block of Acid 62 is way too thin with same sail and fin).