This is how it looks like - its always fluctuating in between 160 and 180.. Is this normal or shoud I do something here?
Only GPU 3 and 4 that always fluctuated? (as shown in your pics) If it yes, you can focus on those two.
Drop until 8 MH/s on each (GPU 3 and 4) isn't normal, you can start with check memory error (since you are using AMD card you can use HWinfo)