Basically, Flight is capped from 1-50. Afterburner can increase your flight cap, and then slotting Fly can improve your speed, but with one 50 Fly IO in Fly, Swift, and Afterburner, you're still capped.
http://wiki.cohtitan.com/wiki/Travel_Powers
Champion 50s (blueside): Marc Bridge, Nicole Bridge, Fred Blaze, Colleen Storms, Sun's Chariot, Moon's Huntress, Point of Pride
Guardian 50s (redside): Connie Mand
AE arc: Spirit Plane Invasion, #29282, @Honbrid
Unslotted, what are the speeds at what levels? Paragonwiki fails me and I can't check firsthand in the game.