500 & 750 final drive gearing same. 80T / 30T.
Interesting. Being a bit lazy this morning have you compared the transmission grearing?
In theory one would typically limit the final gear ratio to roughly the top of the powerband and the gearing of a lower hp motorcycle would be lower than for a higher hp motorcycle (or geared based upon a maximum speed desired) and I assume that both the 500 and 750 have the same redline for rpm.
One of two factors will always limit maximum speed. Either the rpm in high gear (geared so low the engine won't rev any higher) or the hp of the engine (not enough power to go any faster).
In any case there's really no need to go more than about 70 mph and, at least for me, my preferred speed is really more in the 50 mph or less range for enjoyable riding. My favorite roads are often limited to 20-25 mph on the turns and perhaps 40 mph on the straights. I really do love the back country roads along winding creeks and rivers and I never like being rushed to get anywhere. A motorcycle to me isn't as much transportation to get from one place to another as it is a journey. I all too often don't even make it to where I was headed to begin with.