You can run forever at 25mph with 44t gear and it has no problem delivering 35mph at about 8750rpm.
You need 8750 rpm to make enough power to sustain 35mph.
I ran mile after mile at WOT 10,000 rpm with a mildly modified (porting and head) one of these motors only finally breaking a piston circlip from fatigue. I had no problems with overheating (Canada, 60f to 80f) with an improved combustion chamber stock head. Even long steep hillclimbs at about WOT 25mph wasn't a problem. I am 220 lbs.
Where I did have overheating problems was ironically at freezing temperatures due to not jetting for temperature. It leaned out and I got detonation and overheating.
Rusty, you are overthinking all of this. Try the stock motor with 32:1 of a good oil (any oil!) and you will see 25-30mph with the 44t gear that comes with the kit. Heck, my 48cc does 32mph with the 56t sprocket and climbs hills like a charm. Modified stock head, very light porting and a non catalytic exhaust only.