What effect does diameter have? Say like a 14 1/2" vs a 15 1/4? Bow lift, stern lift, propshaft height etc???

Depends on what set up , single ,twin or triple.

On a single u want big diameter so it gets a good bite,on the other ones u can play with it up to a point.
Also a bigger diameter should give u a little more stern lift since u push more blade in the water.
But not 100% sure.

I believe a 15 1/4 diameter prop would get you more bow lift compared to a cut down 14 1/2 - that's how it works on my rig, thats what Bret @ Bblades told me, he would know

Actually, more diameter increases stern lift. This in turn can decrease bow lift if the hull does not have natural bow carrying ability. 1" of diameter can decrease rpm by 300. It can actually decrease it more if the hull rides low and the drag robs HP.

All this being said, use the biggest diameter the boats personality allows. Diameter is a important tool and the variations are endless as well as the changes it can have on a hull when worked with pitch progression and cup heights.

B

In theory If that hull had natural bow lift capabilities cutting diameter down 1" could do the opposite and gain you 300 rpm. True or false?