Thx for the report, this is very helpful.
I'm currently heavier on CPU load.
It looks like your CPU is to slow to provide enough work for the GPUs. CPU load increases with the total solution rate of your system - so this is most likely why your 7card rig is having troubles since it requires more cpu time. What CPU are you on?
It's intel 1151 , G3930 , it's not impressive but it's not on the downside of any processors.
edit. I got such processor on all my machines , and also planning to add up to total of 8 cards on each of them soon , so this might be huge problem to run ur miner @ them
I have same cpu -and don't have problem. 8 GPU in rigs.
Aroud 95-100% cpu LOAD (G3900) on 8 gpu + teamviewer.