It's about the same distance to Littlehampton from Brighton and you can only see the tall bits there.
You can probably see the tall bits to the west of Eastbourne and Beachy Head. Unless you swim a long way out, Sovereign Harbour will get in the way of line of sight to most of the rest of...
The cliffs you can see on the Isle of Wight are about 300ft high.
But going back to the original question, from the end of the Palace Pier, Seaford Head to the east and bits of Littlehampton / Bognor to the West.