Results:
Cards : Vega 64 (aircooled, reference, samsung)
Platform : Windows 10, 18.6.1
Miner : PheonixMiner 4.2c
Algo :
EthashClocks : 1216/1107/875 (ODT)
Actual : 1187/1107/850 (HWinfo)
Stock : 44.75 mh/s
Current Timing --rp 12 --rc 44 --rfc 250 --rrds 3 --rrdl 3 --rcdrd 12 --rcdwr 5 --CL 19 --RAS 28 --REF 15600 :
50.12 (12% inc over stock)
Finally broke the Ethash 50mh/s barrier in windows

Ethash is even better than cn-trtl wrt being able to drop core clock on vega. Where you may lose 5+% h/r on trtl by going to cclock p0 (852mhz), I saw zero h/r loss on ethash when doing the same, at least w/ stock timings. Should allow you to get your voltage down significantly - closer to 800mv.