I have been viewing this thread for a while and thought I'd post a couple of thoughts.
First I have no problem flying an aircraft at it's maximum certified ceiling. For many years the only civilian aircraft to be certified to to fly at FL 510 were Lear Jets. In fact we were given pins with 510 on them that we could wear, I still have mine somewhere. Now even in the Lear 28/29 you could not takeoff and go straight to FL 510, on a minus ISA day you could go straight to FL 470 or 490 depending on the weight of the aircraft, then usually an hour later you could go on up to 510.
Now secondly just because the aircraft was certified for a high altitude did not mean that you really wanted operate at the maximum. Take for an example the Saberliner, all series were certified for FL 450. Now the 40 and the 60 had no problem going to 450 after an hour or a half or so, but the 80 model, forget it, I never got an 80 model anywhere near 450. The 65 could, but only after about four hours.
On the Falcon 900EX it seemed that unless you had really low minus ISA and were light there was not much of a point going above FL 470, on the 50EX 450 was it.
As I was either the chief pilot or a senior captain I always had the other guy or gal wear the mask so I could smoke.
Just kidding now, just kidding on the smoking bit. Kidding on making the other person aways wear the mask as well, we took turns.