Hi everyone, I've resolved the issue:
Bios Settings: I used Bios 0605, set Asus MCE to all Cores, enabled Dual TAU, set XMP to 3600mhz, Gear 1 (1:1), 100:133, manually set voltage to: vccio/sa to 1.2 (vccio was 1.4 with auto, sa at 1.56 auto, way too high), enabled all onboard devices, disabled MyAsus and ArmoryCrate
Windows: completely new setup using the latest available drivers (mostly not using the Asus ones, but the ones posted by another member of this forum here). I use the latest AuraSync Software, iCue and Jacknet RGB Sync for RGB control and nothing else (forget about Armoury....)
Now everything is working stable and fast as expected, thx for all the feedback!