For RX580 GPU I recommend core 1150 and mem 2200 for SMOS. Powerstage will not help a lot to reduce power drawn from the wall. I was using powerstage 4 (default) but power drawn from the wall (7x RX580) was too high for me (1350W) and not acceptable. As long as no undervolting implemented in SMOS I will use ethOS (can undervolt my rig and have 950W from the wall).
with offset whole rigt with 6 gpus should do around 850-900W, but what you are saying is kinda solution as well. I know similar feature should come to SMos as well.
I'm trying to avoid any BIOS modification as possible. Just replaced required straps to get 31MH/s per GPU. As soon as SMOS has undervolting implemented (like ethOS) I will back to SMOS. For now ethOS is the winner.