I just recently had 555RIIs installed in 305/35/20 along with 285/35/20 555tG2s for the fronts; literally on Tuesday morning.
I have some suspension work and the Diablo suspension controller along with a McLeod RTX 1200 clutch and Barton short shifter.
Drag radials, I will never run anything else on the Cat. That grip lets you blast forward with unlost momentum, power and torque thrust with every shift.
The Michelin PS4S is a great highway tire, but very little else beats a DR for outright grip in the lower gears.