i dont know where ur located, but chk out the brian wynn models. the fishcuit is a very fat chunky thick railed board. I didnt like it and Im 190. I ride a 6'0 wynn and i could probably go shorter by an inch or two. i think brian makes better fish than CI.
Not knowing your ability, what you normally ride, or where you'll surf, I'd say the right sized Fishcuit for somebody your size and weight, in relatively small, gutless Daytona Beach surf, would be around 5'6. You could even go smaller, but if you plan on riding it in tiny, weak knee high surf, a bit more foam will help. If you plan on riding it in waist high on up, go smaller for sure.
There are a lot of "Rocket Fishes" on the market, so I'm not sure which one you're talking about. But generally speaking, you want to go a couple inches longer than a Fishcuit, but a couple inches shorter than your HPSB for about the same volume.
I am 5-8 and weigh 155lbs and intermediate advanced adn I ride a 5'-5 x 19-14" x 2-3/8" Round Nose Fish, which is a more performace style fish (less volume) and the board floats me well. The Fishcuit is a more of a retro style fish outline with modern shortboard bottom contours, and it packs tons of volume. Granted a Round Nose Fish and a Fishcuit are two completely different sticks but I would ride a 5'-2" or 5'-4" , maybe a 5-6 to use as a longobard alternative.
It really depends on your level of ability I think. Ride what your comfortable with. A good groveler can stay in your quiver for a long time you will always need one on the east coast.