The unit with the most memory of 20GB = 2x8GB + 2x2GB is not the computer for which I'd rather have that memory.
But I don't think they make 2x2 kits for DDR4. My best bet is to simply double my memory size to 32GB with purchase of an identical kit. Hopefully, that will be almost as good as having a 2x16GB kit, except for a chance I could run the latter at command-rate = 1.
The 2x16 kit likely costs north of $200. the 2x8GB is probably close to $120+. These are TridentZ DDR4-3200 1.35V 14-14-14.
What I discovered was that my caching strategy needs less RAM on the faster DDR4 and Skylake i7-K processor. The benchmark scores are ridiculous. The system trains itself over some period of time to speed up just about every application I could hope to use in a week's time. The Windows Hibernate feature saves the contents of the RAM cache, so the hit rate for the boot drive and the program drive continue to simply grow. For instance the hit-rate for my boot-system drive is about 65% now, and hit-rate for the program HDD drive's SSD + RAM cache is about 98%.
So I can't make up my mind what to do. and if I choose to do it, it has a priority that could delay it several months or longer.