To add to this, mounted speed buffs are being calculated incorrectly at the moment.
They’re using the system that retail has bizarrely used ever since WoD, of adding a percentage of your walking speed onto your mount’s speed, rather than using your mounted speed as the base to calculate from - as it always did in every iteration of the game before Warlords of Draenor.
Fun fact: if you equip a carrot on a stick (should be a 3% buff) while riding an epic mount, you’ll only be going 1.5% faster than you were before you equipped it.
For anyone who’s interested in the details: Mount speed is being calculated incorrectly with the post-WoD method