yeah, all fiji gpus(20+) have a minus 20 hr, plus freeze on 3 rigs at i8.
Which driver version are you using?
What is your -a set to?
I have Furys that went from 345 H/s to 375 H/s (v9.3 to v10.0).
I have Win10 running 16.11.5 drivers with -a 2
Edit: I run -i 6 using stock bios and all stock clocks. Fijis are Sapphire Fury Nitro.