On my bike ride last Friday I just rode the Teesside to Durham part, but I reckon the whole route I mentioned (Darlington - Teesside - Durham - Bishop Auckland - Darlington) would be doable in a day, especially if I didn't ride the Teesside to Durham part via Hartlepool, but instead took the more direct route.
The narrow tyres on my Inbred made it nice and low-friction, which was great for the Sustrans and road mix of trails that we were riding. I span along in a 32:16 gear for most of the ride, just changing to 42:16 for road downhills. It's made me want a singlespeed cyclocross bike now, though. Some drop or moustache bars on my old Kona with narrower tyres would be similar.