Usually it would go like:
reliability first (ECC, up to 512GB RAM, IPMI): C422 + Xeon W 21xx
performance first, cheaper (non-ECC, max 128GB RAM, no IPMI): X299 + i9-79xx
This is also the reason, why they say that the C422 board is made for Xeons. You will lose the ability to use ECC RAM and...