Yes, tyre ratings are indeed very strange.

Also, IF my car does over 150mph, it will be in a straight line.

I wonder if tyres rated to, say, 149mph have to be safe at that speed under a certain amount of lateral force? I wonder if that makes it any better?

I have to say though, as Stu said, I wouldn't want to find the limit of a tyre/s at 150+mph!!

Yokohama Parada's are looking favourite at the moment. I wouldn't mind Goodyear Eagle F1 GSD3's, but I dont think they do 205/40/16's.