Check out this guide, http://vega.miningguides.com/, that helped me setup and get 1950h/s with my Vega 56's modded to 64's. The key thing is Blockchain drivers from Aug 23 and when you restart your computer go into device manager disable/re-enable every vega GPU to get the compute to actually work.
Perfect! Already by seeing the part of the guide where its mentioned a lower intensity of 1800*2 for the card with the HDMI/DP dongle had an dramatic effect.
Simply as step 1, to just change intensity and affine threads to a single dedicated CPU core, I went from an highly unstable hashrate in the range of 3800-4700H/s, I'm now doing a steady:
HASHRATE REPORT - AMD
| ID | 10s | 60s | 15m | ID | 10s | 60s | 15m |
| 0 | 817.8 | 821.8 | 831.1 | 1 | 827.2 | 818.3 | 829.6 |
| 2 | 985.2 | 985.8 | 986.2 | 3 | 988.4 | 986.5 | 986.2 |
| 4 | 961.2 | 959.7 | 958.6 | 5 | 958.2 | 959.2 | 958.6 |
-----------------------------------------------------
Totals: 5538.0 5531.3 5550.3 H/s
Highest: 5738.4 H/s
Still though more to gain on that first card, so I'm gonna test with enabling the onboard GPU and use the DP dongle there and see if the Vega cards pop up (didnt do that with the previous motherboard).
If that works and it gives me and increased hashrate on GPU0, I'm gonna reinstall windows and just follow the guide to the letter
Big thanks for pointing out this link @Xazax310