I could test too if you like.
edit oh n/m, I don't have a watt meter.
No problem I sent you the link though. Keep an eye on the temperatures as it will give some feedback as well. so run at 400mhz on the bitmain firmware at 20% fan speed and write down the temps. Flash the custom firmware and see at which voltage you get the same temps and then lower the voltage to see how low you can go before getting hardware errors.
I haven't a watt meter.