I first do not think that you have an upgrade option here while maintaining the mobo. FX9xxx series processors are not supported for this mobohttps://www.asus.com/Motherboards/M5A78LUSB3/HelpDesk_CPU/
and even FX8xxx series CPU's are not recommended for this board. http://www.tomshardware.com/forum/id-2384030/motherboard-tier-list-am3-chipsets.html?_ga=1.183739045.2005101232.1483893500
And even if you did upgrade, your CPU would still fall into the same general tierhttp://www.tomshardware.com/reviews/cpu-hierarchy,4312.html
Last, I question that this CPU is bottlenecking the GPU, lots of people are getting good pairing results on 3DMarkhttp://www.3dmark.com/search?_ga=1.125869837.161540583.1483814751#/?mode=advanced&url=/proxycon/ajax/search/cpugpu/spy/P/1858/1096/500000?minScore=0&cpuName=AMD
FX-8320E&gpuName=NVIDIA GeForce GTX 1060-6GB
Try that yourself, run a 3DMark benchmark to see if your Graphics and CPU scores are relatively the same.