I think you might have an 8.1 metre boat.
Mine is 8.5 metres, has a double A-frame + secondary radar arch, heavy radar reflector, even heavier 24" radome and is generally a pretty heavy boat compared to some of the Scorpions around. It also has an 80 gallon fuel tank.
I don't know if you have an A-frame and other heavy items but if not then my boat could be perhaps 10 stone heavier than yours plus it has considerable windage.
If my boat is indeed so much heavier, has more wind resistance and there is more boat in the water, I guess this might account for much of the difference in top speed. I understand that to some extent it is a trade off between top speed and acceleration so there is a possibility that it could be a bit quicker but at the expense of "shove in the back" acceleration.
I would be interested to know if there is a substantial difference in weight and the "Christmas tree" at the back, as I might be trying to resolve something that may not actually be a problem!