May I ask why you even need a processor better than the one you have? I don't mean to sound rude, but with how high the price is for the 990x, a cpu that isn't even current gen, it just doesn't seem worth it.
I simply don't see how a 960 would be holding you back. Since you have a water cooler, you should be able to over clock the processor you have to pretty good speeds.
But if you really want or need to upgrade, as others said, since it's the same socket it should work, although you may have to update the bios to get it to recognize the new CPU.