Wyn I have a 2006 27' Grady White 273 Chase (CC) with twin Yamaha 250 4 strokes, also year 2006. I get optimal fuel burn in the 3200-3500 neighborhood @ 32-35mph. The boat's top speed is 58-60 mph at 5500 rpm. But say bye bye to the fuel! The original owner overpowered the boat I think because it was supposed to ship with twin 150's upgradeable to 200's. Somehow he got 250s on there. The beam is only 8' 6" so they look kind of ridiculous!
The props are stock Yamaha but I'm not sure the model, etc.
Goddfadda, that is crazy power for a Grady!!! Must be fun at times as I know I enjoy running quick when weather permits.