For more information on issues like game not opening, not being able to see players in lobbies etc. http://steamcommunity.com/sharedfiles/filedetails/?id=323185654
Once the resolution has been set in-game, this setting should remain even when returning the windows text scaling to larger settings
To disable CUDA/PhysX for this game only, you need to add the executable file (mkke.exe in the installation folder) in the Nvidia tool, and choose to uncheck your video card on the line concerning CUDA. Then you need to launch the game by this executable (mkke.exe), to do that easily you can make a shortcut. You need to be already logged in Steam to successfully launch the game by this file.
Disable second screen (if you have one) in your system settings also reduce the slow-motion effect in some way.
Reducing video settings may help, but it still can occur on some specific stages (Graveyard, The Street).
For AMD users with the program RadeonPro, turning it off may fix the frame rate issue, although it is unclear why (not confirmed by RadeonPro developer, still needs more feedback about the frame rate issue which was reported by only one user so far)