At our site in the UK we are restricted to a max 300ft winch launch. However I
have seen this achieved several times.
Well over 3000 ft is achievable if you use the kiting technique, ie let cable
out slowly when the glider is at the top of the launch but still attached, then
wind in to kite up to a higher level. This can be repeated until you run out of
cable. It is only achievable with a substantial headwind.