Its not your MX cards thats your problem.
I had that problem to.
You only need to download a program called NVFIX.
it can be downloaded from http://www.planetquake.com/ztn/nvreffix/
I had 60 Hz at the beginning, now ive got 100 Hz!
So that made me only capable of having 60 fps.
But now when ive got 100
Ive got 100 Fps.
But thats of course if your computer can handle 100 fps?
Nvidia Refresh Rate Fix is the solve of your problem.
I promise you!