Mike's 9900k won't boot with 4800c18 kit on xmp and definitely no 4800c14. On memory side, not all 4800c18 kit can do 4800c14 bench stable, eventhough it can go 5000+ with xmp settings.
On memory side, good a1 can do 4266c12 but probly not 4800. Some a2 can do both 4266 and 4800+c14, but some can't do both freq at all ..Provided that imc could scale up.