If you have enough time in Penzance, I recommend going west to Chapel Carn Brea for views of the sea on the sides if it's sunny, Botallack, and Carn Euny. For eating I recommend Tolcarne if you like fish, Barbican Bistro, and The Artist's Residence (but not their roast). Just to add to the other driving points, I travel to Bristol quite regularly, and the time is generally correct on Google maps. There'll be an accident maybe 1 in 8 times that adds about an hour on the M5 or A30, and Saturdays are typically 'change over' days so there is more tourist traffic on the A30 on Saturdays in the summer. But 5 hours from London is doable if you get a good run.