I have a evga 760 and fx-8320, I always get dips to around 4 fps and I average at around 29 ,changing the settings does nothing.
I have the same processor, what I did was go into the bios and unlock it and took off power saving. Then I this software to unpark my cores for full performance: http://www.coderbag.com/Programming-C/Disable-CPU-Core-Parking-Utility
This should fix your frame issues. Also make sure you are not overheating as that will cause frame loss as well to the extreme you are referring.
Make sure you have super sampling at 100% and not more.
At what resolution?