"Fastest Long boat" is probably a different question than "fastest creeker", since long boats are not general purpose creekers. They are simply boats built to compete in modern down river races -- with a focus on down-river speed while still able to handle up to class V whitewater in the right hands. A secondary purpose is for multi-day self support trips.
Various race results have boats listed for the winners:
Results | The Green Race
Russell Fork Lord of the Fork Race History
For modern long boats, between the three major players--Dagger Green Boat, Liquid Logic Stinger, and Jackson "Karma Unlimited"--it looks like its mostly about who's driving rather than one being a clearly "faster" boat.