The easiest way to test FCLK is save you current bios config, reset your bios, just set VSOC to 1.25v and FCLK to 2200, if the system posts then great, if it doesnt then try 2167, again see if the system boots, anything that boots fine, boot into safe mode (sign out of windows and hold the shift key whilst selecting reboot) and test with Linpack extreme 1.18, 10gb RAM, 15 passes, you dont want the GFLOPS to be any further than 2 or 3 apart, anymore shows unstable FCLK, maybe needs more voltage, or maybe needs less FCLK, if that passes theres something else causing instability.
With Buildzoids easy DDR5 timings, ive found I cant run the SCLs at 4 unless im running my default timings for the first 4 timings, anything tighter and I need the SCLs to be at 5 or 6, so on my wifes system im running 28-36-36-30, it needs 1.45v VDD and VDDQ, 1.4v VDDIO and 1.20v SOC, the rest is set to buildzoids timings with SCLs at 5, so if youre running 6000 CL28 then unless you have one of the new G.Skill kits, youre not running your kits first 4 default timings and may need more voltage.