Other option of course is to move the fuel tank forward. In a boat of this size, 30L of petrol is a significant concentrated mass. I have 3 tanks - one at the bow, the other two at the stern. I use the bow tank last if I've drunk that much fuel.
Other thought ambling round my mind here - you got a tacho? Your basic setup is not to dissimilar to mine. When I first got the boat it had a way to small pitch prop, and would hit 30 knots ridiculously easily, with me trying to stop the engine going >6500rpm! Changed to an appropriate pitch and it still did 30 odd knots, but it revved at the rated RPM. and didn't try to make 35 knots.....
If you have a tacho, what's it showing at WOT? If not, I wonder if you are running too low a pitch and the engine is screaming it's bits off are you actually taking the boat beyond it's design speed? (is that speed mentioned on the paperwork?)