Shortys work good on Boxes and boats with twins, Single V's can be a lot of time and money to make them work, Your doing 80mph now.. Leave it!
If you really want to spend money. Get the Sportmaster and keep spacing it down. Have you looked at single engine raceboats. They run deep to keep the bite on the prop. better for drives and better in rough water.
My Pantera started at 4.5" with a Bravo lower, Tried -2 Imco and Sportmasters with spacers from .75 thru 2 inch, and LOTs of different props. Ended up back to Bravo Lower spaced down .75 of a inch.

and most of the opa pictures of the class 5 and 6 boats that i've seen looks like they are using a standard lower case.
sure would like to know what x / shaft hght they're running

You know exactly where to put it!

Did you notice pics from the front while catching air. You can see the whole prop