In training for Ride the Rockies, I try to make it out to Skyline Drive in Shenandoah National Park every week. It is essentially 21 miles straight up, and then 21 miles back down. To give it a visual, here is a 3D profile of the route I often take:
Anyway, on April 11, I brought my GoPro and recorded part of my descent. This short video has me going between 35 and 45 MPH. My record speed is 65 MPH, but that was in Colorado on a very different road.