+1 - 39 can be done fairly easily. For reference:
- I've been up around 50 any number of times. Fastest I've ever descended was 52 mph. Hogpen Gap, northern GA. 15% grade, and a mostly straight shot for about 2 miles. I'm a chicken... a number of the guys I was riding with went faster.
- Just the other day I hit 41 on a little 3% downhill grade with a tailwind the other day, and I've done 40+ on flats in strong tailwinds.
- My fastest sprint that I know of is 36.
- My group can run mid-30s in a paceline on flat ground with a decent tailwind.
And those are by no means meant to be bragging... all are only modest numbers. There IS always faster.