I tossed the same question around in the auto-x forum and pretty much got the same answer. During braking, most of the weight of the car is transferred to the front of the car where the bigger brakes are needed most. The stock rears are fine. One recomendation is to get a proportioning valve if you don't have ABS. That way all four tires lock up as opposed to just the fronts. It allows just a little bit more braking power to be transferred to the rears under hard braking. I got my front set-up a year ago from that brakes-r-us place for 429.00 delivered to the door. The calipers don't say Cobra on them, but who cares. My car is a GT not a Cobra. I did visit their web site lately, and they do have better options and far as powder coating and caliper markings.
P.S. the car stops on a dime.
Hope this helps, Flip.