how fast does the gentle lady go without engine

Not very.
20 mph may be possible based on flying one at the slope.

Just a guess but I'd say the speed range is about 8 to 15 mph for a "normal" glide slope range of near stall to reasonably fast but not diving. In a 20 degree dive it'll do maybe 30 to 35 mph and in a vertical dive maybe 60 to 70??? But at that speed I would not expect the wings to stay on for very long. Paul, I think you're being generous with that 20 mph or allowing for a steeper "glide" than my estimate.

Unlike may other model designs the Lady does not penetrate well. Other designs will seem to come up onto a "step" and fly fast with little altitude loss. But the Lady just speeds up in direct proportion to the glide slope with no really noticable max efficiency speed. In other words it's max efficiency is when it's flying just a little faster than a stall.