What Would 50 # of TQ and HP gain get me in a single V hull with 900+HP?
RPMs Gain?
Speed Gain?
Prop Gain?

This is the info you need to get the answer to your MPH question.

http://www.go-fast.com/boat_speed_predictions.htm

This helps... looking for what rpms gains there will be for re-proping. If this is worth doing or not.

I doubt you will need new props for +50 hp. Play with the formula to get the current MPH. Add 50 HP at the same hull efficency & weight = increase. My guess is 1-2 MPH.

50hp usually ads around 300rpms, but being that you are already at 900hp, who knows.

300 rpm is quite a bit if it will pull that much.

Using estimates of 90 MPH(seems like you said your were running around 90) as your current speed and 6000 boat weight, my program says you'll gain approximately 2.5 mph with 50 hp. That equates to around 150 RPM increase with all else remaining equal.

Bob Lloyd
Full Throttle Marine

Boat is 4800# dry + 40 gal 244#, + heavy ass drive extra 100# and extra gear and bodies 500# =5644# about right.

2mph

50 hp may get you broken rods and pistons