Question about gearing for Top Speed

Or maybe it becomes a matter of overcoming friction from wind drag. In which case, you need more HP
Ok , I wasn't sure, but
I have seen that with a 350 motorcycle, published in an FSM, back in the 60s or 70s. So you're on the right track. I just can't help with the numbers.
However; I got this;
A friend and I headed out to BC from Manitoba in July 1975; he on a 750 and me on a 350. The only way I could keep up to him at 75/80 mph was If I lay down on the saddle and hung my ankles over the rear signal lights. A few hours after we left Regina Saskatchewan I vowed to get rid of that lil 350 and a few more hours we came to Tabor Alberta and the first thing I saw was a big ol' Suzuki dealer.
A couple of hours later, I was sitting tall on a brand new 1975 WaterBuffalo! We were flying! and I was sitting tall.....
Now If I remember right, that 350 was rated 29hp, and the 750 was 70hp.
So yeah yur on to something lol.Wish I could help. There was an article in some muscle-rag back in the 90s, about a certain E-body Barracuda that was built to cruise at high speed. I cannot recall the numbers but I think it was brown, and had custom fender flares; does that count for anything,lol. That article was somewhat technical, from what I do remember.