Have you tried running the rig only with the 6 stable GPUs?
Could be the slower one, most of the time, problems are caused by factory defects.
I haven't, but all the GPU's are stable when I run Claymore Miner for ITNS coin... so I wouldn't think there is a problem with the GPU itself ?
Well I take that back. The Claymore miner crashed too. UGH. Guess I will try removing GPU 6 and see what happens