I was in a book store the other day, and came across a cool little book. StarShip Spotting, for all you anoraks out there. Has all the major Star Trek vessels in it from TOS to TNG.
Flicking through it, I saw something interesting regarding the mass of Fed starships. The Sovereign comes in at 3,250,000 tons (or whatever), barely a quarter ton more than the Akira. Come again? Sure enough, the Sovvy is barely larger than the Akira, with the Galaxay weighing a whopping 1,250,000 tons more.
Curious, I flicked through a few more reference books, and sure enough, the weights are consistent for all ships for all references. Apparently the Sov is designed, with the Intrepid, the Akira, and the Defiant, to be a smaller, more efficient starship. I guess, rather than being a galactic exploring porker, like the Galaxy, the Sov is a lean, mean fighting machine.
In which case, why is it bigger than the Galaxy in SFC3? We've lost all the SFB components from the game, so we might as well have canon sizes...