Anybody have a high-speed camera? Maybe we can go "Mythbusters" on it. Get a big wall, and paint alternating white and black vertical stripers, 1" wide. Set the camera up, and have someone do some false casting with a fly, positioned such that the caster is between the wall and the camera, and you can see the fly traveling past the wall. Just count the number of inches in a second of video to get speed.