Any under/over volting? My assumption is that you're modding the clock via Claymore so the answer is no, but you know what they say about assuming...

Also, which driver are you using? When I was on 16.xx I was at 330 H/s for Fury airs, but after v9.1 I rolled back to 15.12 to avoid hangs on opencl calls and lost 10% of my hash.  Each card is now at ~300 H/s.