You won't have any extra power to go 65 mph with a load.. 55 loaded at 2,800 rpm will probably be about all you want to do, or all the engine can do. Then in OD and empty you could go faster, 65 may be OK, preferably at about 2,500 for a little better fuel mileage.
Run the ratios and speeds in the calculator, see what you find?
Grigg
