I'm running an i7-9700k on ASRock Z390 Taichi. It was trivial to overclock the CPU to 5.0GHz, even on auto settings for that board (obviously, it depends a bit on your silicon lottery draw with your particular CPU). But, from everything I can tell, I have about an average CPU. I can run it at 5.1GHz, but it isn't stable under stress test so I backed off to 5.0 with AVX offset of 3 (to keep the heat down under AVX load). Mine is air cooled with a Noctua NH-D15. You can see my whole build here: https://pcpartpicker.com/user/jfrien...d/#view=yrtLJx
if you're curious. I got some nice Black Friday prices so prices will vary now.
If you're into serious memory overclocking beyond the XMP rating of your memory, then I'd stick with ASUS because they seem to have a lot more support here in the forums and in the BIOS for the nuances of memory overclocking. I did get my G.Skill 2x8 memory that was rated at [email protected]
to go [email protected]
on the Taichi, but it literally took me weeks to figure everything out. For memory overclocking, there appears to me to be a lot more support for ASUS Bios settings and timings here in the forum.