50 milers, eh?
I’ll leave you to pore over maps, but my proposal would be…
Back road to Bainbridge, over Stake allotments, Buckden Rake, Starbotton (optional via Buckden Pike and Walden Road), Old cote Moor, Arncliffe Cote to Street Gate, Langscar gate, Stockdale Lane, back across towards Langcliffe via Victoria Cave (FP), BW to Stainforth, Little Stainforth, N to Crummackdale, BW north at Wharfe, Thieves Moss, Borrins, Cam End, Cam Fell, BW/byway off left side of Ten End, Hawes.
Mixture of fast kms, short stretches on road and a few toughish climbs. Might not exactly be 50, but should be enough, really. 🙂
Alternative is to go over Stake but drop to Thoralby, link BWs over into Nidderdale via Braidly, loop round via Middlesmoor, head over towards Buckden Pike (hard going on BWs) and drop into Starbotton on Walden Road again, but head towards Oughtershaw and either go straight up the road before heading into Hawes via Ten End, or extend it yet further by heading straight ahead over to Horton and back up Cam High Road again.
I’d certainly want a big breakfast before either of those.