I walked Pen y Fan a few months ago but sadly it was a cloudy day. I know that Jonathan de Ferranti's viewfinder panorama shows the North Devon coast over 70 miles away to be visible, as well as Lundy Island. Has anyone else been fortunate enough to see the Devon Coast and Lundy from Pen y Fan?
I live in Sedgley between Wolverhampton and Dudley and I have seen Pen y Fan quite often on a clear day from my local hill Sedgley Beacon (often binoculars are needed to see it well). I can imagine that the Black Country Hills wouldn't stand out much from Pen y Fan, though, as they would just look like a faint ridge.
At least you were lucky enough to see the Devon Coast - I couldn't see any further than about a mile. I have heard about the Brecon Beacons being visible from Exmoor. Apparently, Fan Brychieniog (but not the Central Beacons) can even be seen from High Willhays, over 80 miles away, according the High Willhays panorama at www.viewfinderpanoramas.org.