FL200.
FL125 in a TB20 normally aspirated and a AC11 Turbo, over the Alps and in northern France to get over a temporary restricted area when Prsident Obama was in the area.
FL550 at Mach 2, like others have already said over the Atlantic.
I have a friend who is a former U2 pilot. Unfortunately if he told you he would have to shoot you.
FL 265 in a glider. Minden Nevada. Interesting looking down on a passing 727
14,500 in a C172 in Colorado. Mind you we did take off at 10,000…
johnh wrote:
if he told you he would have to shoot you.
And that’s the last we ever heard from johnh 
Kittyhawk wrote:
FL 265 in a glider
I think this one wins
Highest is FL105 in a DR250 coming back from Corsica
Also, lowest is -3 AMSL (BMSL?) at Dunkerque LFAK
