I just figured this out like 4 hours ago.  I ran it at 31 for about 30min and didn't get an error.  I ran it at 30 for an hour and didn't get any errors.  Right now I'm dual mining Eth and Sia at 28Mh/s and 830Mh/s respectively.  This has been running for the last 2 hours and it hasn't had any issues.

Edit:  Forgot to add.  These cards have 4GB of Hynix and 4GB of Samsung memory.  Hence why so many people have had issues overclocking the memory on them.

I just found some Gigabyte RX 570s at my local Frys, so I'm going to try those out and won't be able to test the stability of the XFX today.