I reckon there is a good case for a study of this.. .There is a lack of groundspeed reference at 10000, you could be doing 60 knots or 100 kts and it looks the same.
At altitude in the mountains around Indonesia its not a problem, the only thing you notice is the altimeter and the change of vne, t4 etc, but man, try ferrying it over the water at 13000ft, no way, not this little black duck, very uncomfortable.