How is power consumption out of interest?
On nVidia cards Lyra2z was known to have very low power draw. It sounds like the AMD version could be drawing a lot more as directly poportional to core clock and voltages?
On NVidia cards power consumption like Cryptonight (with light overclock core, and downclock memory).
On AMD cards depends what do you want - if 2.8-3.2 MH from RX4xx/5xx is enough for you, than you can do downclock memory and downvoltage core. If you want get some additional 200-500 kHs per card and you have cheap electricity than you can try doing some overclock core with voltage compensation for stability.