The cruelty of it all is that when you make the front brakes less effective, you require less braking in the back, because of forward weight transfer.

I think that in this case, the only difference (between the GSX setup and the VR-4 setup) is rotor size, and caliper stiffness. For all intents and purposes, the caliper stiffness is irrelevant for everything, except for pedal feel.

The difference in rotor size, however, is about an inch. I think that a car with a VR-4 brake setup would enough extra weight transfer forward that the stock rear brakes would be sufficient. If not, go for a good solution, and get a proportioning valve.

Stock brakes are hideously forward-biased anyways. It is better, for most drivers, to lock up the fronts first. If you don't believe me, crank on your parking brake on the highway and see what happens.

It all comes down to tires, though. What can your tires handle for longitudinal acceleration?