Andy, I called a Michelin Techhead at their HQ. He helped me last year when tyres for one of my bikes were unavailable and the bike manufacturer would not approve Michelin but at the time Michelin had completed their own testing and he sent me an email confirming approval.
So he said he would be reticent to use other than Mclaren approved as the sidewall and tread/compond/construction specification become important at speed and when hot under load, especially high torque load.
However I do wonder if we are talking about performance at the extreme and mere mortals don't get there?
It is an issue on bikes as the tyres work different to CAR tyres in that they have to maintain profile for stability.
However he expected Michelin to go through a testing programme with Mclaren at some, unconfirmed, point.
I have now been quoted £300 for the PZ rears.