Just to update:
Ordered a 3 blade 9.25 x 8 pitch prop to replace the dinged up 9 pitch i had.
Results:
Same load, 4200 rpm. Same Speed 7.5-8.5 depending on bow weight.
I also did a run without a passenger, boat got to 10mph almost instantly and topped out right at 12mph. 4600rpm, I believe...