I guess with the motor mount mods the prop is running at or near the surface which works with your new motor which revs higher than the stock. I don't think this would work well with the stock as I find it cavitates very easily already without bringing the prop closer to the surface. The motor revs way up and the boat slows down. I find mine (stock version) handles best with the motor trimmed in slightly and a 7 cell pack for additional weight in the front. The trim is just right - riding on the back section of the hull but without hopping. Anyway I think the hull should be able to handle considerable speed provided enough of it is in the water and the water is calm. Maybe more power (i.e. more cells) is the solution although this would likely require changing the ESC and maybe the motor.

Also, I was wondering if anyone had any information on taking the outboard apart to relubricate the gears, shafts, and bearings as suggested in the manual. Someone on another forum strongly discouraged me from doing this saying I would not likely be able to get it back together again.