Newton Abbot (NA) to Bude via Moretonhampstead to Whiddon Down (B road) and then via Exbourne, Hatherleigh and Holsworthy (A roads to get the distance; there is a myriad of minor road options, all hillier) = 90km
https://ridewithgps.com/routes/12455020 If you're contemplating 190km, I'd return via Okehampton, old A30 to Cheriton Bishop and thence south down the lovely road alongside the young Teign x A38 to Chudleigh Knighton, to NA
However if weather allows, for preference I'd do a loop over Dartmoor
https://ridewithgps.com/routes/12455492 via Bovey Tracey, Moretonhampstead, Princetown, Yelverton, Lutton, Ivybridge, old A38, Avonwick, Totnes; though maybe clockwise if the wind is SW. I'll be up at Princetown tomorrow morning and may do that ride (from there).
The MTB trails up at Halden are great fun, though I confess only going there in the summer months: we have Woodbury Common close by: its scope is broad.