I would advise you to make sure that 300 hpdi had the series two power head! Not the series one, or you will b in the shop alot

Go to Nautic Star's website. They have a database of performance figures which can give you an idea of how a different size engine will affect your boat.
For example, going with a 300 over a 200 may burn .5 gph more when cruising, but you are cruising 10mph higher at the same rpm.

Smaller motor will give you better efficiency, but only if you are willing to take forever to get there.

2.4 mpg at cruising speed-loaded. 1.5 mpg WOT loaded. Both given on a 24 ft bay boat.

You can also go to Yamaha's website and look at the performance bulletins for their 300 hpdi motor and the hull you are looking at. The performance bulletin for my motor was real accurate. I checked it by logging my miles ran on gps against how many gallons it took to fill it back up. The performance bulletin for your motor/hull will even tell you how many gallons they had in the boat while test was done, how many people on board, etc.

Been left drifting with the Hpdi
and lot were in the shop.
Can't go wrong with 4 stroke 225hp yam.
Worth every penny in the long run when you consider gas mileage, oil, maintenance, and resale/life of motor.

Good luck
remember-most important aspect of motor performance is returning you home!