Testing one of the RX 570's in my system with the FX 8350. Not a bad match. What has really impressed me is the underclocking benefits of these GPUs. 

With no overclocking, only undervolting from 1150mV down to 760mV, it now sustains a constant core clock of 1244MHz (instead of dipping down below 1100 and even into the 900's) and also runs 15C cooler. 

The result is a fairly significant performance gain. 

After testing with Unigine Superposition, 1080p Extreme, the difference between bone stock and undervolted with a slightly tweaked fan curve was a score of 1868 vs 2190. 15% improvement.