Parisianviper, you are asking about the hydraulic and mechanical balance, but on an ABS car, that is not what controls the system anymore.
A 40/44mm diameter piston front caliper and a 43mm rear would be almost the same front to rear clamping force balance as a 38/42 front with a 40mm rear. Calculations of the ratio of front to rear piston areas show the 40/44+43 would be barely fractionally more rear biased, but I would expect the balance to be good. The difference, and perhaps the upgrade, might be moot, since the ABS system manages the braking and overrides the mechanical and hydraulic size differences.
In practice, the ultimate brake stopping performance difference should be zero. The fronts are already capable of exceeding threshold braking torque and locking up the wheels (evidence is that these same calipers easily do so on a non-ABS car.)
Endurance braking events may favor the SRT calipers only if the pad surface area is larger. Larger pads can tolerate equivalent brake heat better than small pads. The braking may still be equivalent (if the smaller pads are rated for higher operating temperatures) but they may wear faster or then be too cold for street use.
Schulmann correctly points out that extended track use will favor the largest pads, which forces you to the largest calipers. Think about that - better track performance is not the caliper size or how many pistons, it's really how large the pad is and managing the temperature of the pad. Having a larger pad that wraps around the rotor more is what requires more pistons.
I think when Shulmann says he removed the proportioning valve spring, he didn't mention that some other proportioning valve had to be installed. Going from a one-piston 36mm, 40mm, or 43mm rear caliper to a four rear piston caliper would generate a tremendous amount of additional rear clamping force and the rear tire would lockup very easily. It has to be throttled down with an adjustable proportioning valve.
Driver perception may change. The added volume inside a larger front or rear caliper means the master cylinder travel (pedal travel) might be very slightly longer and therefore the pedal "feel" might allow better modulation. It's not better braking, but making better use of the braking.
If you have an 01-02 ABS car, then you already have the larger master cylinder that comes on the SRT. I'll suggest this - if larger volume calipers increase pedal feel, wouldn't a smaller master cylinder also? By increasing (slightly) the distance your foot has to travel, you increase your capability of making fine adjustments. I have a good/used non-ABS MC if anyone with an ABS car wants to try it.
