I'm interested in learning how to get the maximum possible height on a
winch launch, without compromising safety in any way.

This question has two parts really - how should the pilot fly the
launch (pretty much how should he operate the elevator during the
launch), how fast should the glider fly, and how should the winch
driver feed the power in? For the sake of argument, let's assume the
glider is a K13.

For reference, I fly from an airfield with a 3,300' long cable, and the
maximum height I achieve repeatedly is 1,700'. Headwind typically goes
from around 10kts at the ground to something like (I estimate) 20kts at
height.