Okay now i ran the ccminer just with one card at a time ("-d 0 | -d 1") etc.
I then tweaked them as much as i liked. I did that with every single of my 6 cards.

I got them all running with core +170, tdp at 120-130W/card resulting in 34-35mh/s. That is looking very promising. So then i removed the "-d" tag again and used all cards together. And for whatever reason they do run with 27-28mh/s again. They all still do have core +170.

What the fuck?