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.

 Yeah, I think it will probably make a decent bit of difference, but it kinda depends on how the movement templates shake out.  You're looking at two extra baselengths in distance each move, which is fairly significant.  You'll certainly be able to get into gun range sooner, but I'm not entirely sure how big a payoff that will be.

 I think it's a bit of a double-edged sword.  The bigger base can you into and out of trouble just as easily.

The Boost ability as well adds a bit more movement. The upcoming A-Wing and TIE Intercepter also have the Boost ability already printed on their cards, as seen here:

http://www.fantasyflightgames.com/edge_news.asp?eidn=3565

…so they are almost as fast, but not quite, so Han's ship is the fastest hunk of junk in the galaxy - I love it when gaming and fiction unite!