There is no performance difference between them at all, they are the same chip. If you run the FX-8350 at the same frequency as the FX-9590 then you have done exactly what AMD did at the factory via binning.
Very few 970 motherboards support the continuous high output, so I agree that your best bet is to go with the FX-8350, assuming the board isn't limited to 95W as well, in which case you would need to get the FX-8370E which doesn't need the 125W of the FX-8350.