Eth mining or dual mining? Eth only uses similar power at stock clocks, and you can downclock a lot, allowing significantly lower voltages, further reducing power.
You can downvolt as much as you want, ETH is always going to be considerably higher on on powerdraw than ZEC.
I could downvolt eth only to use ~80w stock clocks, GPU-Z (not at wall, but same card so it's relevant). ZEC uses similar. If you downclock to say 1000MHz instead of 1260, you get same speed on Eth (zec suffers), but you can lower voltage another 100mv or more, chopping off perhaps another 20w (haven't tested yet).