I've been 70+ on minibikes before. On my drag setup (it's for sale as a roller...) it wasn't scary at all at those speeds. The bike is dead steady even if you let off the handlebar. I was collecting parts for a 236 stroker build for it, not sure if I'm going to go through with it since I'm trying to sell the bike without the engine.
My DB30 is scarier at 45mph than my drag setup at 70+mph.