Try moving the centre of gravity rearwards!
Met a bloke who said his Windy 37 ran faster when he had the jetski sitting on the bathing platform.
Whilst running flat out, get your guests (preferably heavy ones) to move from the front of the cabin to the back of the cockpit, and give it minute or two. You will usually (on most powerful cabin boats) see the speed increase.
If someone sits on the jetski and starts it up, you may be even faster