I was able to get the rig to push 338mhs at Nicehash@DaggerHashimoto, using PhoenixMiner and recommended amdmemorytweak utility inserted in the advanced tool settings on the SMOS dashboard. Great help from the SMOS Discord channel.
BogdanCo settings is even better but my rig couldn't handle it, so I had to settle for 42-43mhs per Vega
You can try 1000 core, 1075 mem @ 850mV with amdmemorytweak --rp 12 --rc 44 --rfc 250 --rrds 3 --rrdl 3 --rcdrd 12 --rcdwr 5 --CL 19 --RAS 28 --REF 15600
Should get ~48.2 Mh/s ETH / Vega64 and stable with no rejected shares...