you need 150 ( epic riding skill ) to learn 225 ( slow flying skill )
and you need 225 to learn 300 ( fast flying mount )
225 cost 800-900, mount 100g (60% speed )
epic 5000g, 200g mount 280% speed
Three known speeds so far:
Normal flying mount = 60% speed-- Bought
Epic flying mount = 280% speed -- Bought
Nether drake/Swift(armored) Nether drake/Peep the Phoenix = 310% speed
Nether Drake - from netherdrake faction, no more info than that there is quests up to neutral standing with them.
Swift Nether Drake - Given to the top teams in each Arena season.
Peep the Poenix - No known information.