I'm currently running an 8x4 prop behind a 16hp
I believe Go devil 16s run a 9x3. Would I get more rpm with a load using a 9x3?

I had a 16hp GD and ran a 9x3 2blade for mud and heavier load at 38-3900rpm@aprox 12 mph and 9x3 3 blade for open water at 3600rpm @ approx. 15 mph. the 2 blade was better for veggie and would crawl in the tough shit and the 3 blade worked ok but not a good in the mud and veggies! I would replace props when they wore down below 8" because loss of speed and digging power!
all on a 16x48 Lowe flatbottom,