The rear base hubs are not compatible with S rotors so it is a major PITA for little or no benefit. I know of no one that has gone that route. Hubs, rotors, calipers, pads, cali bolts, spring kit = $2k plus for a 1% increase in braking forces. To increase rear braking bias most of the spec race cars use more aggressive pads on the rear base brakes. It works.
