+1 for the route from Wotton - that was my old commute.
Personally I wouldn't go as far as Dumbleton, as then you will have to go through Cheltenham or Gloucester, neither of which are particularly pleasant. Instead I'd head along the Cotswolds from, say, Chipping Campden. The most obvious route would be via Temple Guiting, Andoversford, Birdlip, Bisley and Nailsworth, though there is a nasty main road between Andoversford and Birdlip. However this can be avoided if you go to Bisley via Cowley and Brimpsfield. There is an alternative route from Temple Guiting to Nailsworth via Salperton, Withington and Winstone, but this is a bit lumpy in places (particularly around Withington). Both of these should be quiet and scenic.