A dragon flies at 45.32 MPH (74.16 KPH) when at the most efficient flying angle. (When you middle-mouse-click and drag your camera to look all the way down)
However, when flying straight forward and /almost/ flapping, you fly a 31mph (50kph).
I did a sort a proportion (1/124 = x/45.32) and figured out that for every 1 Velocity gained, you fly an additional 0.36548387096774193548387096774194 mph.
I've heard of bipeds that run around 220+ speed. I'm going to estimate that speed is the same as velocity.
220 * 0.37 (rounded) = 81.4.
So bipeds can run around 81mph. (130 kph)
I find this highly amusing.
*goes back to calculating the size of Istaria*
Edit: Flying upwards, you fly at 8mph (13 kph)