I'd like to see how this spins out with proper saddle position... I'm thinking that things will slow down as those legs will be travelling farther when they are moving with proper range of motion.

In the real world I have got up to 180rpm on descents pushing 82 gear inches and maintained a very smooth cadence and secret for this is not to let the pedals drive your feet but for you to keep driving those pedals with enough power to maintain that cadence and pedal contact as if you back off the ride might get a little bumpy.

I have always run a brake which makes bleeding off speed much easier than trying to resist a crank and drive that has that much kinetic energy and it takes a fairly perfect setup and well developed technique to spin effectively at high rpm.

I always say I spin like a gerbil on crack... now I just do it with a lower gearing.