Yeah checked that, couldn't find anything. However my new RAM came today and it fixed nearly nothing... The only difference is that I now can only use 2666MHz because otherwise my System stays black (couldn't even get into the BIOS).
But I tried Titanfall 2 and there I could fix the stuttering nearly completly when I reduced GPU memory and core clock. But it's just fixed in Titanfall and even there it stutters sometimes.... I'm not really sure whats the problem... Should I try Windows 8.1? Just to see if it's software related?