just an update on my settings and results:

have 3 vega's mining ETH on my rig (have a mix of rx470s, 480s and 570s, using phoenix 4.1c, amd driver 18.5.1 but will try 19.2.2 soon)

all vega reference 56's flashed to 64.

using wattman to adjust settings
windoze 10 1803
gpu 1012mhz @ 0.825v
mem 1085mhz @ 0.825v
power limit -35%

previously getting max of ~43.4mhs before winamdtweak changes

now getting between ~49.95mhz and ~50.9mhz (depends on gpu) with :

winamdtweak --i 6,8,9 --CL 19 --RAS 30 --RCDRD 12 --RCDWR 6 --RC 44 --RP 13 --RRDS 5 --RRDL 5 --RTP 4 --FAW 18 --CWL 6 --WTRS 4 --WTRL 9 --WR 15 --WRRD 1 --RDWR 18 --REF 17000 --RFC 248

0 errors over 3 gpus over 13+ hours.  happy to leave everything alone now