So we figured it out

Me and Anmar, late tonight (this morning?) figured out how to fix TF2. Disable Quad SLI. Disabling Quad SLI made the game work PERFECTLY. No crashes, no C++ shit, and no chokes very few seconds!
With SLI disabled, the game still runs great at 2560x1600 with all bells and whistles, so it's not a big loss. What it is though is a big pain in the bum, as disabling or enabling SLI has to be done on the nVidia control panel and can take up to 30 seconds each time. Oh well, at least there's a way to play the game, I was getting mighty annoyed at the upgrade fucking up my favourite tipple.