I was foolish on several occasion. I think bike helmet is bit moot at that kind of speed. At 45MPH or around there, the sound of air rushing around your head is so loud you can't hear much of anything.

At 60MPH, my cheek was flapping from the air, and all I can hear was the sound of air rushing around your head. Then I thought, my helmet is pretty much useless at this speed (if I crash). The other thing I remember was that it wasn't easy to breath with all that air hitting your face. Really couldn't pedal fast enough to get any power into the wheel. Good thing too that my wheels were balanced.

Yes it was a downgrade around 8% at around 7,000 to just above 5,000 feet elevation where the air was thin.