I didn't have the brembo version, but the regular GT brakes version and I didn't care for them. I mean the drilled and slotted rotors look cool, but I felt they did not have as much stopping power as the OEM rotors and pads. They also squealed really bad. Took them off after only 1k miles or so. I upgraded to stoptech slotted rotors with hawk HPS pads am happy with the results. Although I will be installing the 4 piston brembo's soon as I am supercharged and want the look and feel of the brembo brakes.
My guess, from having used ceramic pads in the past and having them (Hawk ceramic pads) on the car now, is that they don't have the initial bite that organic pads have, and that's what you felt. Along with the squeal that ceramic pads produce. I had to remove my Hawk ceramic pads, apply a serious amount of an anti-squeal product, and re-install them to get them quiet.
I'm thinking your solution of the Stop Tech rotors and the Hawk pads is the type of solution I'm looking for too. I like the good bite of non-ceramic pads.
2012 GT Premium, Brembo PP, MT82, 3.73s, Blk/Blk. Bama 93R, Koni Yellow Rear Shocks, Hawk Ceramic pads, Luxurious & Plush Floor Mats