I'm happy to lead a shorter (and more leisurely) variant, getting to Quainton after 20 miles, then following Paul's route back (38 miles in total). If you want to do this please click I'm attending. We can sort out who is doing which on the day.
The GPX file that I have uploaded below can be downloaded into whatever route planning system you use. Sorry I don't know how to post it in an immediately visible format.