Several general rules with props:
1: if going from an aluminum to a stainless prop, always drop down one pitch given that everything else stays the same (ie. the same boat, engine, load, prop style, prop brand). Stainless props are heavier thus harder to turn than a lightweight aluminum.
2. A 4 blade prop with have better load carrying tendencies (to an extent) than a 3 blade, but will also be slower (there’s a few exceptions) than a 3 blade. More wheel to spin, therefor more drag in the water. Pitch and diameter will effect both 3 and 4 blade props differently
3. A 4 blade with have more bite than a 3 blade, but will also cause the boat to be harder to maneuver than a 3 blade ( with a few exceptions)
4. Changing 1 pitch size with change the engines Rpms an average of 150 give or take.
5. No two props are alike. This 23 tempest and that 23 tempest will not run the same nor will they have the same tendencies on the same application. Mercury’s stainless props are machine ground on the trailing edge where as Yamaha’s are done by Mexicans. Ymmv
I know that you are in the business an supposed to know what you are saying, but my experience has always been that for example a 21PSS vs. 21alum. the SS prop will out perform on both ends of the spectrum, holeshot and top end speed due to the flex of the alum. prop. That being said, if you are switching to SS from alum. then you can always go up one pitch, not down.
Also, every single time that I have tried a four blade, it was like I had added super easy power steering to the boat, not harder to maneuver at all, much easier. That's been my 40+ yrs of experience anyways.