Have other people had success with running cgminer with 6 gpus? Is it possible that it's not able to handle all 6 efficiently? This is happening on both my machines. Should I try other things like setting number of threads per GPU?
try -I 9 -Q 2 -g 3 for the start (aggro 9, 2 in queue 3 threads per GPU) as basic don't set anything else and then try through the different vector settings with -v
6970 is just what I have but more shaders... (6950) for me the "basics" work and I do not set vectors by hand, you can have a look what it does when you run only 4 cores with adding -d 0 -d 1 -d 2 -d 3
that's all I can guess from your readings