2nd question, i see baer makes a 13" rear rotor that works with stock braking, if i ran the 13" up front and the 13" in back with the cobra brakes would it be worth the extra dough
Nope, they're good for looks (opinions also vary on this) but for the price, you won't see much increase if at all in stopping distance with larger rears. I looked into that Baer kit alot when I was shopping for brakes but in the end decided to stick with the stock calipers/rotor size and just put new pads and rotors on it and paint the calipers to match the new fronts.
But yeah, you won't believe how ****ty the GT brakes are until you slap-on the Cobra stuff. The difference is night and day, especially on the race course. The MM LCA's did a noticable improvment to the way the car handles the twisties, but the brakes take the cake in this decision.