I have recently test driven a 7.5m rib fitted with a transon lift allowing a 7 inch stroke limit. Out at sea in a 2ft wave height there was no noticable difference in performance in the 50 - 55 mph top end range. In the sheltered confines of the harbour a small amount of hull lift was noticed at around 53mph
With reference to trim tabs, if you replace your old manual "pull out the peg and drop it overboard", with an outboard with electic trim you will not need to fit trim tabs. Go for a 50hp Yammy and your Flatacraft will go like a rocket.