Looks like I won't be getting that GPU voltage down after all. This card does not want to run stable below 1100 mV, which is still okay considering the default is 1250 mV. I haven't messed with mem speeds much, but it was not overly-productive when I did, so I may leave that alone for now. Just running default mem speed + voltage at the moment.
Fully overclocked (1800x @ 4 GHz, DDR4-3466 CAS 14, ASRock X370 Taichi) the system pulls 500W from the wall by way of a 750w EVGA P2.
I got:
Time Spy
7563
Fire Strike
17874
Sky Diver
48976
Cloud Gate
42790
Ice Storm Extreme
188999
Ice Storm
199915
Ice Storm Unlimited
206170
edit: I don't have a link for it, but I got a Superposition score of 14870 (default 1080p medium).