Damn.. trumps me, was going to say 15,000 over mt cook in a duo discus. That was cold, but 36k in a K13? You're braver than me
Also 9500 in a PA28 at MTOW (less climb fuel) on a 43 deg c day - was +20C up there... Couldn't go higher without oxygen, not sure it'd have made it any further anyway!