It seems you could with vega 14nm undervolt a lot without losing hashrate, it looks you cant on vega 7nm as much as you could with vega 14nm.
with such wide bus and fast memory all algos start bottleneck to compute power. So, you'll need to keep gpu freq high => high voltage => high power consumption
Yeah and that is something I dont like. I have a gtx 1070 I did a test on eth and my best result was 800mv, core voltage +0, power limit 52, core clock -250 and memory clock +730, hashes at 32.7mh's, best I could do, 96 watts, efficiency is what I like.
I found a pretty good efficient Hashrate/Watt of 0.55MH/W running the card at 1449MHz giving 75MH/s using 135W of power.
https://ibb.co/9bJN2jvThanks, this is what i like the most, efficiency. Now if only navi could get close to this result then we would have a winner, I think navi will close in around 49mh/s.