i did a search and will keep looking but i was wondering if there is a rule of thumb or average when going for a 4-5 or a 4-6 blade prop on slip drop? have a 31p 4 blade and that im currently getting 21% slip at WOT looking to get this into the mid teens and wondering if its "easier" to go to same pitch with more blades VS more pitch same blades

A 29 pitch 5 blade will lower the slip numbers or a 27 pitch 6 blade. The only issue would be can your drive Handle the extra "BITE" you will get with the extra blades.

ya, i gather more blades more bite. but im wondering if there is a way i can "guesstimate" my slip. im trying to target min to low teens so wondering - short of trying a bunch of different props, if there is a way to accurately narrow it down

It doesn't really work like that.

Your propeller will not be exactly 31.0000 inch pitch, so the slip number cannot be compared from propeller to propeller.

But more blades means more bite.

There is no rule of thumb for this scenario. Changing number of blades also comes with altering blade shape, diameter, blade thickness and so on.

Gary Stray once said something in an interview that really changed the way I thought about props in regards to slip.

I don't remember the exact wording so I'm paraphrasing here but he said he doesn't get caught up in prop slip numbers or trying to chase a specific number. If the boat is fast and it handles well that's all he cares about.

There's a good probability that adding blades will reduce slip a few percent but not gain any speed.