My Gainward 750 Ti arrived today. My mining rig has now GPUs from 3 different vendors and it is working under Win 8 x64

I have the onboard Intel 4600 (with connected display), a AMD Radeon 6950 1 GB for mining (395 kh/s stock clock, scrypt) and the new NVIDIA 750 Ti (290 kh/s stock clock, scrypt).
Driver installation was straight forward. Only downside to not having a display connected to either card, I can't use CCC or Nvidias control panel. If I would want to overclock I have to first connect a display.
You can do it with either MSI AFterburner, EVGA Precision and Nvidia Inspector (but yes the nvidia control panel does not open).
I am thinking also about adding a 750ti (my psu should still have 50watt to spare even with the two big cards)