That gain on Vega is because 900mV was too much to begin with. I was running my vegas stable with 800-812mV. For 5700 xt, you can lower you core clock to 990-1030 Mhz depending on the memeory clock. This will allow you to go below 700mV on the core voltage.
Hi, you have a nice tutorial how to do this on YT, and also Vega cards can be made more efficient.
THIS IS HUGE!!! TeamRedMiner v0.9.4.7 R Mode is Awesome! Is 5700xt now the most efficient card?