I just rendered a video using version 4.2.2 and it looks like the GPS calculated speed is way off (by about a factor of 2).
Here is the original GPS data: https://www.dropbox.com/s/t30n2a041t194ij/September10Flying.gpx?dl=0
And the rendered video: https://www.youtube.com/watch?v=kpj1y8qVIKg&t=43m40s
The speeds it calculates are super slow--like half I'd expect. Google Earth says it had a max speed of 115 mph, but the VIRB output shows nothing close.
Could this be something to do with rendering at 60fps instead of 30?