I decided to go for PSS 255/35/21, 295/30/21 - these tires are the closest to the stock 255/40/20, 295/35/20, the diameter difference is 0.1% or so.

Maybe 295 width is not the best choice for 700+hp Panamera. But i'm sure that 295 Michelin Pilot Super Sport anyway better than Pirelli Pzero Nero GT in 325.

Also 21" x 11J wheels weight is definitely lower than 22" x 12J - this is important for unsprung masses and for 100-200km/h results.

 

There are 325/30R21 size for both the PSS and PS2cup. I know the PS2Cup does not perform as well as the PSS in the wet but you stated grip is important so I suggested that. Even on stock turbo with full bolt ons, the PSS slips when launched.

http://www.michelinman.com/US/en/tires/325/30/21.html

 

The overall diameter of 325/30/R21 is 13mm more than stock wheel. I'm not sure that it's ok.

 

Also there maybe a problem to setup 325/30/21 Michelin Pilot Super Sport because actually PSS is wider than any other brands. 325 PSS is like 355 Pirelli. It most likely will rub over deep compressions.

 

@dhh

Very interested in your wheels and tires. Are they still available? If so, please contact me, i'd like to purchase: 619-818-5191