Check out:
Yamaha Outboard Motors Home - Outboards, Boat Motors, Marine.
The Yamaha web site has performance bulletins that will give you an idea of where your boat should be.
Yamaha has a F-300 monster at 822lbs.
Your F-250 is 604lbs with an RPM range between 5 - 6K
Big difference and your boat is limited to 750lbs.
For comparison: The Yamaha V-Max 300HP 2 stroke weighs in at 539lbs with an RPM range of 4.5 - 6K.
OC Tim's boat runs the upper end of RPM at WOT with a 19 inch prop. If he changes to a 17 inch prop, his RPM may jump to about 6300. Not good for the motor!
I went from a 15 inch prop with max RPM about 6000 to a 17 inch prop with a max RPM of 5600. Since the motor is rated 70HP at 5,500, I figured anymore RPM would be useless and I would use more fuel. I keep the 15 for a spare.
Many ways to build a boat.
One other question, does the boat list or pull? I had to adjust the trim tab on the motor to counteract the rotation of the prop. When the lower unit is trimed up correctly, I can remove my hands from the stearing and the boat will track straight, before the adjustment, the boat pulled to Starboard.
Hope this helps.