Hmm, I think that the first time I installed Linux Mint 18 Mate 64-bit on this box, with the 16GB SSD, I had the single 8GB DDR3-1866 DIMM @ 1600 OC 6%.
I then over-wrote that install with the CloudReady install, which worked fairly well, except for the lack of HDMI audio, which was disappointing.
So I pulled out another 16GB SSD, installed Mint 18 Mate 64-bit again, and this time, I had 2x2GB DDR3-1600 installed, still at the same settings (I believe) as the single DDR3-1866 (meaning, that the DDR3-1600 was OC 6% or so, but timings were de-rated to 11-11-11-38-2T, which is what the single DDR3-1866 was set to).
This time, with 4GB RAM instead of 8GB, the Mint 18 Mate installer created a 4GB swap partition, instead of an 8GB, leaving some room free on the SSD this time.
Also, I tried some different 1080P VP9 videos this time around.
I tried a 1080P VP9 @ 25 FPS, and there was a commercial that was @ 24, also VP9 apparently, and they played without dropped frames.
I also tried another VP9 @ 60 video. It was dropping a lot of frames, but it was still playing more-or-less smoothly, which was an acceptable experience to me, unlike when I tried it the first time, and it would play, and pause, and play, and pause..,etc.
So, actually, the Linux Mint 18 Mate 64-bit experience on this hardware isn't as bad as I thought I remembered. Maybe the dual-channel does make a BIG difference?
Either way, I guess I have a choice now. I think that I would rather put Linux on there, for some flexibility, they can use OpenOffice, etc., and my wireless adapters work in Linux. Plus, they can use Software Manager to download some games if they like.
Edit: Btw, scrolling does seem smoother with dual-channel RAM installed too. Or maybe it was the driver updates, I don't know. I still haven't tried installing the proprietary AMD drivers, but now that the videos on YouTube are playing acceptably, I don't think that I'm going to bother.