(I've not read most of above, just your last reworked plan btw, so apologies)
"Day 3/4 Coed y brenin MBR, dragons back, tarw"
Do 'the beast' @ CyB instead of MBR and dragons back. I takes in 95% of the singletrack sections (excludes dreamtime) but the distance is a fair bit less. Get a map of the loops, and then on the dragons back/beast you want to cut out the big out/back loop (at the far away end) just after the (non FC) cafe and bomb up the road/(3rd) fireroad (on RHS) instead (the short bit of singletrack on that bit is supposed* to be a dull loose gravelly up anyway). It'll make it more doable in a day
Then the next day fitting Tarw and Penmachno (at least loop 1**) should be more doable
*or so I'm told
**IMO (and I'm sure many will disagree) loop 2 isn't that great (when compared to loop 1) so if you're pushed for time (and packing up/driving/unpacking in between 2 forests will take a little while) then IMO you could leave out loop2 @ penmachno
You'll want to do Nant-y-arian before Cli-mach X so you're not having to drive south (but defo do ClimachX, its brilliant, one of my favourites, made better by adding in the steep/loose hidden DH just after the last singletrack section .. )
Coed Llandegla won't take all day, but it'll let you get home I assume. Its a bit different to the others, but probably worth going (so long as you go with an open mind) just to try it to see if you like it if you've not been before