maximum wind speed
FFF, guess I "forgot" about the Concorde!
Further research indicates that at that sort of altitude(37k), the jet stream seldom exceeds 175 knots, but I have yet to find the maximum recorded. Given that the typical cruising speed of the 747-400 is given as 492 knots(Boeing site), this would give a theoretical maximum ground speed of about 667 knots(767mph), so I guess I had a way to go!
FYI, the maximum recorded wind speed on a land-based recorder(Mount Washington) stands at just over 200 knots.