Nice game. I always wonder how you can pull this off in one minute. What is wrong with ...c6?
nothing really wrong with it, in fact the slav (2...c6) is the most common defense to the Queen's Gambit. It's solid, but might not be the best choice in bullet, especially for a tactical player. The immediate c5 forces an open game.
White should probably play 7.cxd5 in the game, leaving black with either an IQP or an identical pawn structure where white is ahead in development.
I have always thought that ...c6 is more tactical (Meran, Botvinnik, Cambridge Springs) and that ...c5 (Tarrasch) is more positional: isolated pawn etc.