-i 19 seems to be the sweetspot and get rejects low (ccminer/enemy-NVIDIA)

-i 21 goes to beast mode but unstable and could get your PSU rekt (use sgminer-brian-AMD instead, add -I 21 --thread-concurrency 1024 --gpu-threads 2)

d=16 minimum diff for x16R as per yiimp pool, so if you are at suprnova just remove it since ocminer said no need to set diff - the stratum servers will take care of it in the backend.

If you have VEGA cards, you will need AceNine sgminer instead.