What is the altitude record for the F/A-18 Hornet?
I can tell you my experience during my stay in Zaragoza Air Base in northeastern Spain, in 1998. After heavy maintenance work, the twin-seater was ready to fly. In order to check all work done, we did a parabolic flight in clean configuration (no loads under wings or fuselage). It was a flight test so we decided to push the limits a little and see the real capability of the General Electric F404 engine. After acceleration and trying to maintain the best angle, we were able to climb up to 63,000 ft.
It was quite difficult to fly the plane when crossing 45 or 48 thousands (I don't remember well), so we decided to connect the auto-pilot. The auto-pilot can handle the plane easily at those altitudes with such low air density.
I recall the last portion of the climb was a nice parabolic trajectory in zero-g (you cannot imagine how dirty the cockpit was, I could see a pencil and some screws from maintenance floating in front of me, among some other things) until we regained positive g's in the descent. It was an interesting flight, but as stated by others, not practical at all from the combat viewpoint.