Roads around that bit of Cornwall are mostly a bit rubbish - either big through-routes with lots of speed limits (A390) or really tiny sunken lanes with no sight lines and few passing places. You definitely need to be happy reversing a few hundred metres if needed.
Fortunately if you head on to *actual* southwest Cornwall it gets a lot better. The north coast road from St Ives to St Just via Zennor is spectacular, and over the moor from St Ives to Penzance isn’t bad either. Starting from Helston the road down to Lizard is pleasant and sometimes quick (well ok, very occasionally quick, but it’s worth it to visit Kynance) and the B3293 across Goonhilly Downs has a mile-long, generally empty straight that is perfectly designed for, erm, driving at a sensible and law abiding 60 miles an hour. For example. Goonhilly is the home of various satellite/comms projects due to its exceptional levels of quiet, so you can see how appropriately a Lotus exhaust would fit in there.
Other things: there are some good roads around Bodmin Moor but again there’s a lot of sunken stuff with poor visibility. The north coast run from Bude to Watergate Bay has some great views but between April and October you’ll probably be mostly viewing the back of a caravan doing 35mph. Finally the North Cliffs road from Portreath towards Hayle is often quick and you can stop off at Godrevy to see a cove full of seals, which isn’t something you can often combine with a decent road.
Happy driving - if all else fails, drive down to Lands End so you can say you’ve driven to Lands End.