SVP makes as much frames per second as you wish.
Then video renderer (madVR, EVR, ...) sends this to the display device. Here's a conversion from 24 / 48 / 60 / 120 / XXX fps to the actual screen refresh rate.
Projector only accepts 60 fps on input (actually it's limited by HDMI).
If renderer gets 72 fps on input and should make 60 fps output it will simply drop 12 frames.
And finally projector itself can make 120 fps from 60 fps input with some kind o FI.
24 fps source -> [SVP xN] -> 24*N fps -> [video renderer] -> 60 fps -> [HDMI] -> [projector x2] -> 120 fps on the screen
So true 120 fps now possible only with selected 120 hz PC monitors (DVI connection). I don't know if there're any TVs / projectors with DP (Display Port) input 