In reply to nicnic:
Dartmoor tends to stay pretty minging after rain for a day or so if there's no breeze. If it is actually raining, it'll be horrible. Haytor area is in the rain shadow of the moor to an extent, so seems to get marginally better weather than the west (Dewerstone area), but is still high so is a poor choice on a bad forecast.
BBC's forecast for Sunday looks alright for Bude, so you might get away with something on the culm.
Some routes (Sarcophagus etc.) stay dry in the rain at Chudleigh.