Thank you rednoW for sharing your reg file. Its the first where iam able to boot into Windows. Both Vega56 with 64 Bios runs at 2kh/s with ~140W for a minute or two and then the AMD Tool crashes or one GPU crashes and resets to default settings. Also if i reduce mem to 950mhz and rise voltages to 1100mV its unstable. Bad luck in silicon lottery?
Something not mentioned in hellae's guide (but is mentioned in the comments), and something that I've lost a whole day to - you may need to up the voltages to 930mV. One of my cards would cause BSOD with all the reg files that I've downloaded, and even at 920mV - even with quite conservative clocks. Now runs rock solid for days on end at 930mV with fairly high clocks. I am sure it does affect consumption, but it is not like I have any choice!