Yeah I have noticed that CPU-Z, AIDA64 and HWinfo64 all give me different voltage readings on my 9900k and Maximus XI Formula. CPU-Z reads 1.144V load, AIDA64 1.344V load, HWinfo64 1.250V load. From my talks on here and the ROG forum I believe 1.25V load is the correct reading. This is at default settings btw, but with some motherboards like mine they exceed the TDP to maintain 4.7Ghz load, so I'm not sure if that voltage is different across other manufacturers default settings.
Since you have a Maximus XI motherboard as well if you just want 4.7Ghz you can just load optimised defaults, enable XMP and click "YES" to the prompt. That will let the motherboard know to maintain 4.7ghz under load and won't power throttle.
Primary System Specs: Lian Li PC-O11 DX - ROG Maximus XI Formula - Watercooled Intel 9900k (4.9Ghz) - Watercooled RTX 2080 Ti FE - G.Skill Trident Z RGB 3200Mhz CL16 32GB - Corsair RM1000i PSU - Samsung 970 EVO 2TB NVME SSD
Secondary System Specs: Fractal Design Define S2 - ROG Maximus X Code - Watercooled Intel 8700k (5Ghz) - Watercooled Strix GTX 1080Ti OC - G.Skill Trident Z RGB 3200Mhz CL16 16GB - Seasonic X-1050W PSU - Intel 600P NVME SSD