Uh-oh.  Going down the rabbit hole here. 

Motherboard allegedly supports fast RAM but I've read that the CPU will only support a max of 2133Mhz DDR4.

Task Manager reports however that I'm running 2666Mhz so what should I do?  I'm just gonna get 2 sticks of 16Gb (as it is only an interim measure and I don't want to blow a hole in my wallet) but I'm assuming 2x 16Gb @ 2666Mhz will be 'safe' as it appears to be currently stable with that speed? 

4x8 is better :-)

Okay, fair enough. 
For a total of 32GB, would I be better off getting two matched pairs (4x8Gb) of just one (2x16Gb)?

...and finally: is chaining a CD Drive and two SSDs on one power cable ok? I guess it is otherwise Corsair wouldn't supply 'em.

yeah that's fine :-)

Fiiiiiinal question here:

My mobo manual says it supports DDR4 RAM up to 2133Mhz.  Is that it?  DDR4 is available at much higher speeds is it not?  Maybe that's all that was available at the time?...

Any clue as to what I could go for now?  Just looking to boost this rig a bit before the build in Dec.