I'm not worried about speed at all. I have a 96 stratos with a 175 hp motor. It seems like I get 4 mpg. I can be on plane at 3200 rpms that pushes alot of water. At 4000 to 4500 rmps can be on pad 1 to 3 people respectively. and then 5500 rpms going 64 mph. What rpm range is best for gas mileage