Coo! You lot are quite pedantic about tyres. The only thing I look for is a bit of tread and that they are round and pumped up. I could understand all this bollox about speed rating if you had fast cars that corner really well but come on. When you are looking at a car to buy, do you check the tyre reference letters and numbers with the same detail as the chassis?
I mostly agree with the speed ratings as you say for Defenders ... but I do check the markings for age of tyre, that they are all the same type and size and I also check them with a pressure gauge! They're the only contact with the ground you have so they are pretty damn critical, even at slow speeds ...
Having said that, the main topic is mostly, it appears, to be in that grey area where the discussion is at or about 100 mph and what rating suits. When I had cars that did those speeds I made damn sure they were as highly rated as possible, as well maintained as possible and in good condition ...