A lot depends on the peroid of the waves, as well as the height. An 8 foot swell at a peroid of30 seconds is an up and down ride, but does not slow you down.
The cat excels in short steep chop up to about 2 1/2 feet. We had 3' chop in our bay from "northers" up to 50 mph of breeze--where it is about 12 miles from the ICW to our house. In that case with a very sort period--lets say 8 seconds, we would go faster to be sure to have kept as much of an air cushion as possible. We crank the speed up to about 35 mph and get on top of the waves--so in that situation faster is better.
The Tom Cat does not have enough tunnel clearance. My Caracal cat has about 6" of tunnel clearance at rest, and it does not close the tunnel. Thus it rides as well or sometimes better than the longer Tom Cat 255.
The Tom Cat does not do well at slow speeds into chop--lots of "slam" and spray flying...