Is there that much significanse to HT/HS if one oil has a 3.2 HT/HS and another oil has a 3.5? It seems the ideal HT/HS for a performance car would be 3.5 or greater. So if your a M1 user, 0w-40 would be preferable. Interesting how the Mustang Cobra R uses a 0w-40, but Corvettes use a 5w-30 M1, which only has a HT/HS of 3.2. There must be more to it then just these numbers.....