I'm running into the same issue. Also in Windows 8 64-bit with a GTX 670. Uninstalled and re-installed game. Tried Safe Mode too and no luck (ran for about 3 minutes before crashing).
The first time I launched it I was able to get all the way through the first mission. Right now I'm at the part where I'm supposed to go to the Dam. Wondering if it has something to do with loading the saved game or something. Submitted a ticket to Ubisoft, so I guess we'll see what they say.