It's good to see that this little ITX board can still handle 9900K @ 5.0GHz very well.

The 6-phase VRM is able to hold up to 200W CPU power package as seen in Prime95 v26.6 Small FFTs (non-AVX):


VRM temp is 61.5C max, measured through IR thermometer (might not be accurate though):


Realbench v2.56 (AVX):


Cinebench R20:


XTU: no throttling during the benchmark



* Setup pic, I actually put one 120mm fan blowing towards the VRM area just in case. 

Next up would be RAM OC.
Look at the RAM OC profiles available in the UEFI, should be useful as a good starting point for RAM OC:

CPU Load-line Calibration (LLC) set to Level 8 (highest for ROG), this will give the least vdroop/vdrop.

CPU Load-line Calibration (LLC) set to Level 8 (highest for ROG), this will give the least vdroop/vdrop.

Not an apple to apple comparison bro.
My highend custom wc is always better than AIO by 15c.
On top of that, you have to take account of the variations in every chip, different vcore required, different mobo (VCCSA, VCCIO settings), uncore, memory speeds, chassis airflow etc. All these factors contribute to the heat as well.