I don't think paladins have 492% mount speed. I don't see how thats possible in any way. Even if Crusader Aura multiplies your 310% that will only add 20(62%) giving you a total of 372% and I thought it just added to your 100%, so you would get 330% with epic mount and Crusader Aura. Plus it doesn't stack with anything else as far as I'm informed.
He's right, I read a few forum posts on the matter and basically it adds 310%+100% together and then multiplies it by 20% for an additional 82%. 496% flying speed... mind blowing ain't it lol?
edit: Also to check this, go to your general stats on your character screen.. there is a "speed" line which will tell you what you're currently going.