I have a book at home, to do with unusual weather, and there is a recorded instance of unusual weather (probably some sort of inversion) where the French coast was fully visible from the hills behind Hastings. Apparently individual coastal towns were visible with the naked eye.
That fails to take into account the height of the object you are attempting to view... the hills on the East of the IOW are at something like 200m, which raises the distance you can see.
You can defintely see it from the Dyke.
You can defintely see it from Worthing pier. From Worthing you can see quite a high piece of land (seemingly a long way out to sea) as you are basically looking at Whitecliff bay and the chalk cliffs near there.
From Brighton, the strip of land would...