1100 mph!
Maximum possible speed. I wonder what happens as he goes through the sound barrier. I couldn't access the part of the site which might have explained that.
Maybe, being soft and flexible, not much.
There seem to be a lot of considerations - deflecting exhaled breath so as to prevent the faceplate from getting fogged, stronger valves against zero atmospheric pressure, frostproofing the valves, and there are more.
Neglect one thing, and the next guy may be the one to make it work.
Gotta admire him.
Arf