I'm running an 88 250 offshore with the 305 I/O the only time I've ever really seen it struggle to plane out was with 6 people on board and 120 gal. Of fuel in the tank, other than that mine seems like it has enough power for a 5500 lb. boat, I've never topped it out but it'll run about 25mph at 3400rpm give or take depending on weight...... As for the fuel well either way its still a v8 : / ill use any where from 15 - 25 gal of fuel depending how far I run.