The road racers on the vette forum run faster times at road atlanta on 275's square vs 315's square. Same compound.
Contact patch for a given weight is always the same square inches.
Doesn't surprise me, bigger tire requires more heat before the compound gets to it's optimal temperature. It is very important to match that for the given situation, autox, endurance, drag, etc. That said, a softer compound on the 315 setup will likely be faster and not overheat.
