I had the Bill special brembos setup under the stock gts 15" for a while. Once they were bed in and worn enough to throw the backing pad back on they were phenomenal. The rear is kinda sorta a bbk now too because I swapped from drums at the same time haha.
My favorite modification of all time is the SS brake lines though. I just love the feedback it gives.
What have you got in the front now? Stoptech?