I did have a serious worry about the movement speed and I'm hoping the mounts don't increase speed more than double a normal trot. I keep seeing videos and the players seem to move quickly. If this is part of testing and things will be slowed down later?
I also worry about movement speed, but the good news is so does Joppa. The pendulum has swung back and forth in testing. On one end we could simply outrun anything at will, on the other end anything could catch us even if we had a major head start. I'm sure the pendulum will settle somewhere nicely in the middle.
I also think that character movement speed (mounted, buffed, or otherwise) is all relative to the size of the world. Thronefast is pretty huge, and it's just one "zone." Without any speed buffs it can take almost 10 minutes to run from one end to the other...if you could find a straight line path you might be able to do it faster :)