Oh wow, so this might make for a much quieter, cooler card. Can I ask if you adjusted the power limits or just the voltages to get here?
I've been tweaking the Core voltages and power limit to achieve cooler running, but with some reduced performance. I guess this is because the core voltages weren't actually being applied as I hadn't touched the memory voltage, and it was running into power limits. Hmmm, there's more to play with before writing this off as just a hot, noisy card then.
To do 1630Mhz locked solid (stock boost) in benchmarks I need between +10% and +20% for stable, and with 1100Mhz HBM2 clock (stock is 945Mhz). It's at 950mV GPU core (down from stock 1200mV). At these voltage and clocks, it is stable down to -10% power limit, there is just some throttling; unlike Fiji which once you start overclocking (or making sure it doesn't throttle) will suck almost whatever power limit you throw at it, Vega it just seems to need the little extra occasionally. I think people are just used to Fiji and some extent Polaris - hence why everyone (including reviewers) are throwing +50% at it; completely unnecessary at least in my case.
My card, at these settings, lies about half way between a 1080 and 1080Ti (much closer to the latter in some games), and less power consumption than a stock 1080.
I suspect it's partly the bad early drivers and need of firmware revisions, but I have to step up voltage quite quickly even for 10Mhz increments above 1630Mhz. There shouldn't be the same kind of process 'wall' as with Zen, at these lower clocks - should be thermal limits. Will see how it behaves once on water, but I don't think the drivers and firmware are really designed to be efficient beyond the stock clock yet ...... and it is ridiculously efficient at stock clocks (HBM OC'd) once undervolted.