Standard subaru 4 pots are cast iron and retain alot of heat and have a small piston diamater. Brembos are alloy, have a larger piston area and pad size and dissipate heat a lot more effectively. Big difference.
However, if you are going to uprate your calipers for track use, I would recommend also upgrading to two piece disks with alloy bells and powervane type rotors as they are much lighter and much more effective at shedding heat, thus reducing fade.
I upgraded to compbrake pro-race1 4 pot calipers and 330mm disks with alloy bells and they are simply amazing. Before I would have to come in every 6-7 laps and let the brakes cool, even with red-stuff pads and racing fluid.
With my current set up, fade has been eliminated during track use, I can stay out as long my tank's full and I have shaved seconds from my lap times.