With 8 cores and little other CPU usage I get 575 kH/s on my i7 6700K @ 4 GHz. I don't know the typical performance
on AMD CPUs. Comparing with other AMD users is probably the best way to make sure your mining at optimum performance.
Yes other users are reporting 300 to 350 kh/s too. I think that is kinda low for an 8 core at 4ghz.
The i7 6700K is a little superior to the fx 8350 but that difference in hashrate is almost double

Maybe if we compile the miner on our machine we get better performance?