I can't seem to find anything for VCCIN on the Maximus X. in HWMonitor the only voltage above vcore is VIN4 and its over 2V.
EDIT: Apparently kaby/coffee lake don't have vccin as they don't have a FIVR.
Yeah it would seem so. I guess the board or CPU controls the inner CPU rails but if that's the case how do you know what your LLC is doing? I used to directly apply voltage to the CPU socket and you could see it in the input so now it goes straight to vcore perhaps?
On Asus boards 6 should be a tiny bit of droop, it is for me and for most people.
Asus uses Intel's LLC spec but modifies it much like using an offset for vcore.
The scale goes from 1-9 IIRC but it may start at 0, I can't quite recall but the 1-9 thing is 0-125% so 6 is pretty much the same as Auto which is/should be Intel's spec or very close.
Why they used 1-9 to configure 0-125% is beyond me when they could have just used percentages.
Definitely keep going towards 5.3GHz, since you're binning. You may find that the lowest voltage at 5.0GHz or 5.1GHz is unstable at 5.2GHz+, due to non-linear voltage stepping near the maximum ambient clocks.
Wish I would have tried 5.4GHz before to see the difference... but ohwell. Currently running 1344 prime @ 5.4GHz 1.45V and the hottest core is 75°C
5.3GHz @ 1.41V (59 61 65 67 67 68 avg 64.5) 1344 prime short run (15.33°C improvement!)
5.3GHz @ 1.35V (57 57 60 60 58 61 avg 57.16) cinebench 1693 (.03V lower than was acheivable for a run before. I got bored and didn't try any lower.)