Actually, putting on only the fronts made my braking worse than the stock PBRs. You'd have to push the pedal very firmly to even have a chance at braking at a moment's notice. And even then, there was no confidence as it felt as if the vehicle kept wanting to move. With that in mind, I rarely let anyone drive my car and had to take extra steps in calculating when I needed to brake. Driving in the rain (with the brakes being wet) was worse.
It hasn't rained here yet but based on my dry driving conditions with the rear setup, which came with a vast improvement in total braking, I have no doubt it'll be improved. My random ABS issues have been solved as well.
I am using the stock GXP brake lines on all four and brake pedal feel has improved (pretty much back to the stock GXP feel, maybe even firmer - I'll have to drive someone else's GXP in town for comparison).
Front only calipers will really mess with the vehicle. Contrary to what others may claim.
Also I am lowered. What other suspension upgrades would you suggest? Bilstein coilovers?
Heim jointed control arms coilovers are always good.
06 GXP | 222/227 cam/cartuning turbo kit on 8psi/meth/e85 coilovers/ still on stock trans at 130k