After getting used to the pump I keep at my parents' home which reads one bar low, I unthinkinkingly continued to compensate by filling my tires one bar over after I came home.
On the descent from a 750 meter climb. my overfilled rear tire blew out at 70kph. The tubular tire blew right off the rim and locked the wheel. It was a miracle that i managed to stop the bike upright.
I don't think the altitude will make a big difference, but the heat from the rims on long hairpin descents will make a difference. If you overfill the tires they just might blow at high speed.