LG 34UC80 Overclocking past 75hz with Freesync enabled

I recently got an LG 34UC80 and I'm loving it - running on a Radeon R9 Fury X. I have used CRU to get the Freesync range to 33-75 and I'm interested in overclocking the refresh up higher than 75hz. I have been been able to add additional detailed resolutions above 75hz, but when I do, the AMD settings driver reports "Freesync Not Supported."

So what am I missing? After I add the resolution, Windows allows me to select the higher refresh, but if I can't use Freesync with the higher refresh, it's not worth the trouble. Any way to get a higher refresh and still have Freesync working?

Thanks for any input you may have!