Overclocking
The ASRock Z490 Phantom Gaming ITX/TB3 showed quite a bit of headroom for overclocking, at least for short runs of wPrime. I was able to achieve 5.3 GHz at 1.38 V core voltage. However, longer runs were not stable. Overclocking is mostly limited by temperature, as the 10 core Intel Core i9-10900K will overpower any ambient cooling solution. Depending on settings, the system will either crash or severely drop frequency.
For memory overclocking, the ASRock Z490 Phantom Gaming ITX/TB3 did fairly well, reaching 3900 MHz at XMP timings and voltages on my Trident Z Neo kit, and it was able to pass my MemTest 64 validation without errors.