I don't think it should matter because I also have modded hd7950. I had some problems at start. Afterburner showed +0 voltage at slidebar but it should show +956. So I restarted the computer and then it worked.
I restarted it too, updated drivers and so on, the problem might be in my end still. I don't know and I give up, RX 480 saved me from investigating further lol
I'll put my R9's on Ebay because I can't keep all of them