Finally figured out how to reproducibly get undervolts to (mostly) stick on the blockchain drivers with Afterburner and Wattman

1) Apply clocks/volts in Wattman. e.g. 1130/850.
2) Launch AB with no adjustments set. (+0mV)
4) Launch Claymore and wait for the miner to fully kick in. Observe your voltage in AB (that you set in Wattman) get completely ignored.
5) Change your Wattman clocks to, say, 1135Mhz and apply (then back to 1130 and apply). Observe the voltage in AB go back to a static, undervolted clock.
6) Note the ∆ in AB. E.g if I set Wattman to 850mV, it might be reading 937mV in AB.
7) Adjust AB voltage offset but don't bother applying it yet. It won't do anything. So, to go from 937mV actual we'd want -90 offset in AB.
8 ) Stop the miner.
9) Apply AB voltage offset.
10) Launch miner. You'll see your voltages jump up again, so do step #4 again. You should now be pretty close to your desired voltage.[/li][/list]

I've only seen it reset to high voltage occasionally when doing something like turning the monitor on/off. Step #4 resolves it.

With this I'm seeing ~5-10W per card improvement over 17.7.1 dualmining.