Need help determining most efficient fuel speed RPM for this boat with planning hull and gross weight is 10 tons

Powered by 2 Mercrusier 454 , with Borg Warner velvet drives.

We have an 87- Planing Speed!! Now that is Funny
I usually run about 2000RPMs- I will push to 3500 sum times But she is a Big Beeeeach

First pic is On Plane

454's, there isn't one. lol Have a friend with gas engines.
I just sea trialed one with 425HP 3208 cat diesels. Cruise 25 mph at 1mpg topped out around 30 mph. (owners log shows 1mpg average) This will probably me my first diesel purchase. These boats are the size of an early 80's mobile home.

No way it will even get plane. It will just push the water out of the way.