[racer_d]

While I don't find the base brakes "lacking" at the track, It would make sense that larger brakes provide better effectiveness for repeated high speed stops. The larger size (overall diameter and thickness) allows for better heat management. Not sure the cross drilling is good or bad.. 1) decreases swept area of disc but 2) should offer better cooling and allowing gasses to escape better than regular "flat" dics.

Rotors, Brake fluid, brake pad material and air (for cooling) and tire brand and size as well as suspension and overall weight, all effect a cars braking ability.

But in answer to the first question -do GT3 brakes fit? I am sure they do fit with some modification. I don't believe them to be a simple "bolt on" swap.