It is a very rare day I would disagree with James. But there is enough difference in the boats which I believe makes our experiences different,
The difference between the 255 and the 24 is the engine bracket. The 24 has the engines mounted directly to the hull. The flow of water at the end of the bracket in transition from displacement to planing has increased turbulence, because of this bracket. I was trying to get the boat to plane at a lower speed, and we ended up with a significant increase of water coming over the bracket with the Permatrims as we slowly transitioned from semi displacement to planing mode.
As the boat came up on a plane, the Permatrims worked as in monohulls or a cat which has the motor mounted to the hull. I did not feel that the Permatrims gave a decrease in the lowest planing speed. The Permatrims decreased the top speed a small amount. This is with the Suzuki 150's which I feel are the best engines for the TC 255. Speeds with these engines and the type of props they use (4 blade, stern lifting, higher pitch), are higher than with the Honda's.
We live up near the head of Perdido Bay--there is about 12 miles of fetch during a "norther"; Winds up to 50 knots. As we left the ICW the waves were close to 3 feet. The only way to successfully get up the bay with minimal discomfort, was to take the speed up to over 35 mph--to get this air cushion increase. The 4 blade props and "reverse" (Counter rotation engine on Starboard) engine mounting all help to give more stern lift.
I agree that the tunnel height of the Tom Cat (either 24 or 255) should be about 6" higher. You have a lot of experience in the 24. I have only driven one a few times. So I certainly believe your experience is valid for the TC 24.