In reply to Garston:
For Wen Zawn, this depends on where you abseil from. 50m will get you down to the ledge at the start of Britomartis. The huge block at the top of Quartz Icicle can be used but needs a 70m rope to reach the zawn bed. I've seen folk use a stake a little bit further along the top & that would need a 60m rope I think. If you use the abseil station mentioned in the guide books, which is reached after an easy scramble (but possibly un-nerving for some), then a 50m rope will get you right onto the high tide-washed ledge at the base of P1. There's plenty of rope on the ab station as well as a maillon & krab, but if you wrap the rope around the block: 50m won't reach the ledge.