Do you hit the rev limiter? If you hit the limiter a Microtouch rev limiter will allow more revs if you have the power to spin the prop faster, if not a slightly lower pitched prop will help along with drying out the pipe a little. It's a fine balance to get more rpm, too much water in the pipe and you'll get good mid range, a little dryer and more rpm, a little too dry and you cook the coupler hoses. If you can find a 95 800 waterbox valve it has 5mm threads on the bottom and you can add a jet to restrict how much water going into it (back pressure), just remember that whatever you do to extract more power/rpm will require verifying the fuel/air settings, a little rich will rob power and a little lean will rob your wallet.