Multiple GPUs with Mavericks for video editing?

[Caramanos2000]

Hey guys, I currently have an i7-4770k running at 4.0ghz on water and an EVGA GTX 670 FTW. I was wondering if I could add an additional GTX 670 to my system. I have no interest in multiple monitors but I am looking for improved rendering in FCPX which is my main use in this system. OSX Mavericks is currently 10.9.

Edit: My version of final cut is 10.0.8

 

[Caramanos2000]

Or would it make more sense to swap to ATI video card(s)? Im currently getting between 68 and 71 seconds with the Bruce benchmark.