Don't worry mate as I had a dyno about 3 weeks ago. Mines got full stainless zorst and pop charger and mine only managed 257BHP mine is an 05 roadster.......
You can actually lose power on the bolt on mods like I have done and not forgetting the older the car gets the more horses you will lose.....
But hey who cares, as it's a great car...... so enjoy it..........