When using the mounts keyring, one cannot put a very fast mount into the Stat Mount location unless there are other stats. So a player cannot use a very fast mount but look like a slower one? Isn't that one of the points for having a Mounts Keyring in the first place?
It doesn't matter. All of your mounts are upgraded to the speed of the highest-speed mount you have used, ever, regardless of what they say on their inspect window.
Nice, I just tested it and my mounts are all speed 85. Good to know. (I think I'll still ride the fast one to travel just to show off)