You will get all the extras you get with the Premium Edition in a digital format (so manual, map, etc in documents form) plus a digital version of the CE Artbook plus the choice of a free game from GOG. You won't of course get the other stuff exclusive to the CE version, but out of the digital distributors I think GOG is your best bet. The stores selling hardcopy versions of the game are offering exclusive dlc like the Roche commando jacket but I haven't seen anything equivalent from the digital suppliers.
GOG's version is also DRM-free. However, I do know that Steam seems to be offering all the digital edition premium stuff too (though I do not see any mention of the digital artbook with that version, I think that is exclusive to GOG), however they are not offering the free game and you may find it harder to cancel the preorder from them (though it can be done, as I mysellf have managed it).
Post edited November 24, 2010 by FlintlockJazz