Audax rides

Might be worth looking at the route of London Oxford London. Although that takes you to Ruislip, which doesn't give you many great options to get back into town.

I'm comfortable with the Gerrards Cross section onwards, but does this look like its a sensible enough route back from The Dean?

Looks ok, but that first bit of the A40 isn't very nice, but it depends on whether you're doing it after finishing or after a night's kip in the Travelodge. Also depends on your attitude to main road bashing.

Watlington to Marlow is a traditional crossing of the Chilterns on Audaxes, but there are plenty of variations to choose from.

Here's a not very sensible route back from the Dean:-

https://www.strava.com/activities/162789149

I went out to Aston Clinton on purpose (as I needed to push the ride out to 100km so I had a control in Aylesbury), and to do that climb.

2008 was my first proper year of Audaxing. My legs were shot. The Dean was the hilliest thing I'd ridden (and was my second ever 300). Fixed of course. It was cold on The Dean that year, a thick blizzard climbing up through Broad Hinton towards Marlborough. Clocks went forward and I think I finished at 3.45am or something silly. Had a hearty breakfast (well, whatever the Little Chef could provide) the next morning by the Peartree Travelodge and set off in lovely sunshine to ride back to SW15. Looking at the finish it seems I'd forgotten (but luckily remembered eventually) about needing a final cashpoint receipt (back in the old days of those DIY perms).