I was wondering if the i7 9700 non k could support above 2 channels at 2666mhz. I am considering upgrading from my i5 6600k to this as i have found one in a old computer that i would only need to get a 9th gen motherboard to use.
Many of the various mainboards will allow elevated RAM speeds via XMP profile, yes... (certainly the Z-series mainboards will)
You are better off with your RAM kit in a pair of 8 GB or 16 GB sticks vice a quad stick kit, as the former are generally at higher clock speeds/tighter timings, and more importantly, less expensive than quad stick kits. (mixing a pair of two-stick kits to get 4 sticks is a gamble)