Be careful when you talk about 2 pot, 4 pot, 6 pot calipers.
The effective diameter of the pots and rotor diameter is what is important.
I am running 2 pot 3.37" in the front and rear.
The 06 2 pot impreza front is 3.37"
the 06 4 pot WRX has 3.082" front
The 06 4 pot STI has 3.386 in the front.
The 06 1 pot impreza has 1.5" in the rear.
the 06 2 pot WRX has 1.5" in the rear
The 06 2 pot STI has 1.417 in the rear.
I have more than twice the clamping force as the wrx or sti rear brakes.
With no portioning valve and square tires, my rears lock up just before my fronts. (this is a bad thing)
I am installing my wider rear tires and will test again. It problem remains the I will add proportion valve on rears.