For what it's worth, our cars suspension was designed to have the big bag of 13" wheels under it.
Most of my pleasure motoring is on less than perfect country roads, & some far from perfect back roads. On the country roads my 7, on it's 13s is a much nicer car to drive than the 8 on it's 15s. If I am going to be on those back roads, I don't even consider taking the 8. On the other hand, if I will be on good quality smooth grippy roads, the 8 is the choice.
Of course stiffer springs & shocks on the 8 have something to do with this, but those big bags of 13" soak up a lot of imperfections in the road.
My Honda S2000 is OK on the country roads on it's 16s, as it was designed to use them, but it is not a good car for those back roads.
I suggest anyone thinking about low profile tyres on a TR 7/8 think first about where they will use it. Sometimes what looks good is bloody awful in use. If you are going to the track, great, if going rallying, not a good idea.