Thanks for the replies folks. Some people have commented on weight. In my OP (quoted above) I said that I leave the lock at the place I lock the bike, and also gave a link to a very heavy chain. I'm sorry if I wasn't clear, but weight isn't really relevant (except in so far as a very heavy chain could possibly damage the frame). The journey is only 4 miles, I can either take the lock/chain in on my first trip, or make a special journey in the car.
What I was more interested in is whether very secure locking devices, like the two "anti-angle-grinder" locks I mentioned, are more of a deterrence than ordinary gold or diamond rated locks.
I suspect most thieves don't know enough about locks to recognise the anti-angle grinder locks until they find they aren't getting through them. So probably not a deterrent to them making the attempt, but much more likely to scare them off before they complete it.
But as oters have said, the gold standard locks are plenty for almost all insurance policies (not all even require that level), and after that it is just really a case of how important your specific bike is to you personally.
If it has large sentimental value, or is a model which would be very difficult to replace, then I'd be more willing to spend a lot on protecting it.
If not, I'd do no more than insurance requires, and let them replace it if the worst happens.