Distance: 133km, altitude: 1277m.
https://ridewithgps.com/routes/29624905
This route takes in Brill, to warm you of for some more bumps on the way to the Chilterns. The return journey follows the Phoenix Trail, an abandoned train track, which is partially paved, and partially crushed limestone. When riding it early April, it was absolutely fine on a road bike. It may proof more of a challenge in the winter.
Cycle routes in and around Oxfordshire 