You wont do bad anywhere on the Cornish coast Martin, although personally I find the further west you go the more dramatic the scenery gets. The north coast gets the best evening light and few of my favourite places would be - Godrevy lighthouse at Gwithian (Nr St Ives), Porth Nanven (St Just in Penwith), Sennen cove and Lands End which has spectacular cliffs.
On the south coast - The Lizard, Mounts Bay, Newlyn/Penzance, St Michaels Mount.
Not sure what it'll be like in a weeks time but lately alot of these places have been rammed with tourists. Porth Nanven will probably be the quietest as it's the most difficult to find.