Running a 10hp backwater on a 1442 with the 8x6 prop that came with motor.
I set governor speed to 4000 rpm out of water.

I know motor is a little undersized for boat but we have a 9.9hp restriction in our area.
Motor can only get to 3300-3400 rpm wot with just me and fishing gear.

wondering if I need to drop to a 8x5 to try to get rpms up and maybe squeeze out another 1mph or 2 ?

You are right, a bit underpowered with that hull, but worth a try with one size smaller prop. For example, my 27 HP LT is rated by most mfg.'s to use a 9x7; I get that 1 mph more with a 9x6...I am slightly over sea level so not saying this will be the result. Worst case you have a suitable backup prop, everyone needs a spare prop at all times.