Sounds dreamy, especially the pushing up boggy stuff, haha!
May head to Helensburgh for early evening, pedal 30 or so miles, camp and then see how I get on the next day. Don’t mind 15 hour days, I’ll be alone so not like I have much else to do other than ride my bike.
You seem to be a lot fitter than I am but some of it is bloody slow going. Big boggy hills and such that you'll need to push up especially on GK SKs.
Also it's nice around there. There's a couple of good beaches for a mid-ride dip and the pubs will be open again. So I'd vote 4