I ride on Schwalbe Marathon Supremes. Both different sizes.
A 40 on the rear, because you really can feel a more comfortable ride with the fatter tire on the back. It has no effect on the better steering on the front. Both tires at 92PSI
A 35 on the front, because you really can tell that the steering is more precise, and quicker, and more sure footed, with it on the front. It has no effect on the soft ride that the back provides. Both tires at 92PSI.
I know, because i have tried them all different ways - 40s on both, 35s on both, 35front-40 rear, 40 front-35 rear.
I run them at 92PSI, because you really can tell the difference in the roll, vs 85PSI.