I'm using an asrock z370 extreme4 to overclock my 9900k and was looking to overclock.
if it's already possible with your current platform what would be the point of upgrading, just "to overclock"?
do you mean you are just not satisfied with the results on the Z370?
what benefits will I get from going from z370 to z390?
nothing noticeably different performance-wise on average.
some support some faster memory kits, some have more M.2 slots available, but nothing that would make it worth the money.
if you're main concern is better performance, you're only smart option is to upgrade the platform and CPU to a Z690 with a 12th gen.