Get new pads??

You might as well try them out and see how you like them, unless you are using them for track days I would think they would work fine.

It might be worth buying pads that are meant for track use and switch them in for the days that you plan on going to the track. Good track pads usually require some warm up for them to work well. I assume that by your list of mods you are capable of putting brake pads in yourself. The GT500 weighs about 400 pounds more than your car, so they should do ok if you don't feel like buying different pads.

it is your money but i would have gone with the stage 2 kit from brenspeed. i know a couple of guys that have it and cant say enough about it. good luck with what you got, but on the other hand this comes with all four rotors and the better pads. not to mention the brake hoses

http://www.brenspeed.com/mustang_2005/brakes.html

In my opinion, the brenspeed kit is kind of a rip off...... All you get is pads rotors and lines... You can get a set of earls SS brake lines from summit for like $125 and a set of pads from anywhere (Hawk HPS + for example @ tirerack) $84.00 front $74.00 rears. Rotors are just as easy to find and you are best just using new take off rotors you can get for like $40 for the front and about the same for the rears. Sure you may wear the factory rotors out faster but you can get 4 sets for what the rotors on brenspeed cost you for one.

On the other hand, with the GT500 setup you get 4 piston calipers that are easier to change the pads in (In my opinion) stainless lines come with the kit as well as all new hardware. If you are going to track your stang a lot you can't go wrong with them. Plus more pistons = more braking forces with more heat dissapation of the 14" rotors.

Although, it is not my car so the final decision is up to you.

In short, run the pads that come with the kit. If you decide you don't like them or race a LOT for long periods of time, then through them out and slide in a new set of higher performance pads.

DOh.. Quoted myself.....

The GT500 kit is a great middle of the road option. I wish someone would come out with a floating rotor kit for that though.

I think your best bet would be to get some pads that are good double duty pads and then a brake duct kit, I find that mild race pads make the best double duty. Those combined with the bigger GT500 rotors should keep fade from being an issue.
Dan