My understanding is that for a 53MY the stock prop is 28 x 30

As I have posted in a previous post recently I had a bent up prop, and bought some from SKY that are 28 x 28, I got them on and all vibration is gone, and they work great!

I just dropped off the bent set to a local prop repair place and they found the stamp on the old ones to say 28 x 31......

So, on our trip bringing her home we got 1.25 MPG, running about 1200 rpm and 9.2 knots.

New props at 1200 rpm seem to run a noticeably amount slower I think I'm getting 8 or 9 mph (yeah not knots) but yes slower.

So I am wondering if it really matters for fuel economy?
If my thinking is correct, I might need to bump the rpm up to achieve the same 9.2 knots, but that should take the same HP and therefore the same GPH correct?
If I am looking at this correctly it should theoretically be a slight bit less torque on the motors and thus be a little easier on the motors?

I'm not planning on running on plane, so let's remove that from the equation.
Just wondering about mileage and wear and tear on the motors.

Your thoughts?