Thanks to their over-sized bases, these ships get much better distance returns out of the movement templates. Consider where the front of your ship is at the start of your movement to where it is at the end. Because X-wing uses a "front edge to back edge" alignment for movement, this means that large ships get more effective movement.
That makes me think that, in terms of raw speed, getting the Boost action onto a YT-1300 would easily yield the fastest ship in the game, validating Han's boasting about his beloved Falcon. That Engine Upgrade card is looking better and better.