So...
In otherwords, when you stick you arm out of the window and the forces get higher, you could (theoretically, and if the car could fly) increase your altitude and the forces would reduce (assuming constant speed, not IAS). Therefore as you went higher, you could go faster and keep your arm out of the window as the air pressure reduced. (read no bits falling off). Eventually new contraints would begin to take place as you got faster and higher, these would be related to compressability (super sonic air related) rather than air getting out of the way?? Here then, your arm would still get the bad end of the deal because of the pressure effects of air becoming super sonic?
Surley though the air is still passing around and over you at 320kts (as indictaed at the barber pole, not super sonic) even though the mach reading is .99999 etc
Sorry, still a bit confused.