I have 1.58 drives now, with props being too big I went 78@5100, I am looking at a set of #3A that are 1.68, would that bring rpm up? I think so and may put me at my goal of 54-5500 easier?

I asked my drive guy and without doing the math he thought between 250-300 revs

Gary Kolofsky to the white courtesy phone :-)

Just by doing the math you’ll gain about 325 rpm to maintain the same prop shaft speed

But, you have more reduction, it’s easier for the engine to pull that, so you may find a couple hundred more if they’re happy running there

Hmm so might be a good move, and I am ok with similar performance I had before, just don't want to lose any.

Go to BBlades site and use their slip table. Plug in what you ran with the old and then just change the ratio and run it again. Slip shouldn't change but speed will.

Showed slip change not speed

Whats the pitch of the prop?

Use this one , you can calculate any variable:

https://www.mercuryracing.com/prop-slip-calculator/

That one is a good calculator seems if I just bring up rpm 300, things would be same overall, so going to a 1.68 isn't horrible it seems, price is very right for 3A to go that way

BBlades shows that with 28 pitch props, 1.58 gears, 5100 rpm, 8.86% slip boat to run 78 which is reported now. To change to 1.68 gears, same props, same slip and same 78 mph, rpm will change to 5422.