Based upon the speeds of my 790 in various gears, I doubt if it matters. One would just have to reduce the throttle speeds to slow down or speed up.
This might be a problem with older tractors, but not for newr (1990 and newer) geared machines.
So...in answer to your question about hydro vs. gear...it wouldn't matter.
I wouldn't run a tractor in 4WD on paved roads...hard on the drive train and tires.