You all forgot the fastest stock one, Fantic Motor, GT6 on road Caballero off road, that would hit 50 without any tuning, my mate did carry a toolkit and spare crank in his backpack though
I was always a 4 stroker, so S550 no pedals and a nifty 90 head and barrel, plus a Dunstall power pipe ran under motor to stop passenger burning legs, it did me a 12 mile each way commute for a year no worries at speed.
Then a Honda CD175, the BSA replica with rubber and chrome tank panels and a bathtub rear mudguard, replaced with a Yamaha YDS7 250 with Amal 32 carbs, twin leading front drum did nose wheelies, and would lift the front in 5th all day long, those were the days.