The outrageous frame rates are obtained by disabling vertical sync. This unlocks the video card from the monitor's refresh rate. It allows for frame tearing. Sure, you may read 700fps (or whatever other silly high number people claim) but remember 2 things:
1) Your monitor is still only displaying at it's refresh rate.
2) Your eyes are still only capable of seeing 30fps.
The best setup is one that allows for good average frame rates. If you can get it so that you are getting a constant 60fps, you're far better off than the guy that gets 100fps in the clear but drops to 15 in the weeds...