Just thought I would share my benchmarking of the R9 nano.

All power measurements were done at the wall to be 100% accurate.
Benchmarks were done with  Claymore ZEC - v8.0 (-i 4)

Stock:
1 gpu: ZEC: 272 h/s Watts: 200w

-100mV ROM
1 gpu: ZEC: 211 h/s Watts:  91w

-125mV ROM
1 gpu: ZEC: 217 h/s Watts: 90w