Since it's a dead socket, your only option on x99 is Broadwell-E, which is not really worth upgrading, imo...unless you're going to get use out of more cores. In that case, you can throw an 8 or 10 core in there (or more if your board will take a Xeon).
6950X 10 core is a beast upgrade. Or even an 8 core 5960X is a good upgrade, and can be had for relatively cheap.
I would not purchase an X299 system just yet either if you are primarily gaming. Performance is CPU heavy games actually took a backslide compared to Broadwell-E, and even compared with Haswell-E in some cases. The refresh will hopefully fix those shortcomings.