Which ever prop gets you to 5000 RPM
with 6 people, you are probably in the 13p-15p range. you will need to test.
your boat is over 6000 wet, not including people. so you are at 7k+ if you have change in the pockets
my old searay had the same motor, and only weighted 3000 dry, about 3600 wet, with 4 people I was running a 19p. I thought my boat was underpowered.