I've been trying to find a mini-dp1.2 - hdmi 1.4 cable and have failed to do so. I found one company that makes them, but I cannot figure out how to buy the product. They were going to mail me one for free, but that never happened. They "claimed" it would handle 4k @60hz, but I haven't confirmed that or found anyone else that has.
The issue you will face is not FPS, it's the frequency that is accepted and allowed. At 30hz, you'll only see 30 fps, even if your card does more. Gaming at 30hz is aweful.
Hopefully, these graphic card companies come out with something soon... this tech has been around for half a year now.