Finally got around to properly overclocking my card under water in the full new build. My GPU seems to take a bit more voltage than most, requiring 1209mV at 2101Mhz (which maintains ~2050Mhz in games) -- stock was 1117mV. I also can't seem to do 1200Mhz HBM -- I get artifacts in windows almost immediately -- even at idle temps of like 26C for memory!
Anyways I am getting 10,242 in Timespy, and 24,820 in Firestrike. Seem some people get quite a bit higher with 1200Mhz HBM. It is surprising that HBM clocks matter that much -- surely the card can't really need that much B/W and it must be memory latency improvements with higher clocks..? (+200Mhz on HBM clocks adds roughly as much b/w as a RX 580 has in total!)
Vega absolutely loves bandwidth, it seems to be the primary reason why VII is so much faster than vega 64.