39.x MPH
It was on about the biggest descent I have here with a long straight run out after. I think I have one which is steeper, but it might be a tad shorter. I know for a fact the steeper one has very bad pavement though. I don't want to attempt anything crazy on bad pavement or on twisty descents.
I was mashing pretty hard to try to get up to speed. I was hurting by the 50x16. I spun down the hill in my neighborhood in the same gears feeling much more fresh - next time I won't throw the chain into the smallest cog and go. I'll reattempt and shoot for 40+.