As far as I know, the Bake Bias settig in GT3 has no influence on overall braking power. It's simply a case of how much of the load is applied to any given pair of wheels.
This of course means that brakes set to 1/1 should stop you in just the same way as those set to 20/20.
Does anyone have any empirical evidence to back this up?
That aside, how you bias the brakes is entirely defined by your driving style and the underlying handling nature of the car.
Now, I found the RGT to be an unwieldy pig on tyres that were too grippy (e.g. T5's) but discovered that by setting up a rear bias in the brakes and applying just a touch of deceleration mid-corner she became a much nicer behaved lady.