I would absolutely recommend the STI Brembo kit. It's made for the WRX / STI. From all the research I've done, aftermarket Calipers not specifically tailored to your car can increase stopping distance. Why pay $1000 + for that?
I have Wilwoods 4 piston kit on my car. I will never recommend it to anyone. I kid you not, my caliper cracked right in the middle. No seams or bolts or anything there, just cracked in the middle of the face of the caliper. It squirts brake fluid everywhere. I'm getting the replacement this week, but seriously this is supposed to be a high performance brake company. I've never even heard of a factory caliper doing that.
Probably a fluke, but still, I'll never buy their stuff...after I spend this $250... for one caliper replacement...
355 awhp fp green six speed wagon in Corvette Atomic Orange