>>725371207
I'd give a number but it's been so long and I played a lot with scaled up stuff that changed atmosphere size.
I recall 2/3 altitude was good enough for mun->kerbin run without popping out or having it spicy enough to burn antennas and other pokey bits.
The real fun is doing a direct ascent from the surface (no circularizing around the mun) and getting the trajectory right.