The Asus boards seem to have a bit more vdroop than others, but on LLC 7 it's manageable. On mine it droops about .05-.06v at full load regardless of voltage. So if I have it at 1.30v it might droop to like 1.25v. Dunno what the deal is. It is somewhat annoying. Behaves the same on manual and adaptive. At 5.1GHz at 1.305v adaptive LLC7 (AC DC LL @ .01) I droop to 1.252 vcore under load. The peak vcore reading, similar to what it would be idle on manual voltage, is 1.296v. VID is meaningless, especially since I'm using adaptive voltage at the moment, but it reads around 1.309v under load and drops way down at idle.
Why are you using so much voltage? If you have to push anywhere near 1.40v for 5.1Ghz you probably shouldn't bother. You likely just got a less than ideal chip. You won't be able to cool anything north of around 1.37v under full load without a custom loop or extreme cooling anyways. I know, because on mine 5.2GHz was looking like it was gonna take around 1.37 or 1.38v and I stopped pretty quickly after a few stress tests and benchmarks. There was no point other than to set a score or something; it made zero sense for 24/7 use. Just run it at 5.0GHz at a lower voltage and call it good.