I once drove a Bedford mini-bus that had a bench front seat, so no adjustment. The windscreen was rather lacking in height and I had to hunch down as much as I could; this gave a view that allowed a speed of about 25 mph, or 30 if the road dropped away a bit.
It was ideal for motons as there was never anything to avoid - couldn't see it, t'ain't there. I like to be able to stop in under half the visible or actual clear road.