Interesting...
FWIW, I had the opportunity to drive my Z with Invos at COTA. While the soft sidewall is quite noticeable on the track, I thought they were very predictable with decent feel in the full range of cornering. The same day I drove another Z with the V12s soft sidewalls, and I felt like they did as good as the Invos during mild cornering but suddenly got mushy during heavy cornering with no warning. Terribly unnerving in someone else's car.