Pads and discs are definitely the first path for upgrades. If you are a regular downhill driver (eg: mountain drives), then good discs are an absolute must to reduce the chance of warping. Personally I use DBA HD-series discs (which are derived from the slotted 4000 high-temp series popular as track discs, just without the slots).
As a test, when you think your brakes are running out, find a piece of straight road and deliberately jump hard on the anchors in an effort to invoke the ABS. If ABS does NOT engage or only engages very slightly, then your pads are simply too hot and cannot bite the disc properly - get pads with a higher temp tolerance. If the ABS kicks in too quickly and easily yet you're not really stopping as well as you were 20 minutes ago, then it's not your brakes that are the issue, it's your tyres - they've gotten too hot and have run out of grip. When you run out of grip, the wheel slips and ABS tries to compensate.
Other things you can look at (these do not preclude better discs, pads and tyres):
- Upgrade your Master Brake Cylinder and Brake Booster to a wrecked Impreza WRX STi unit - one of the simplest and cheapest bang-for-buck mods you can do to pump no less than 13% more fluid to your calipers for the same amount of pedal pressure.
- Braided brake lines - reduce flex in the brake line hose, resulting in more pedal force transferred to the calipers instead of flexing hoses. As a result, gives a firmer brake pedal, increasing confidence.
- Master Brake Cylinder brace - reduces flex in the firewall when pressing on the brake pedal hard, resulting in moire pedal force transferred to the calipers instead of flexing the firewall. As a result, gives a firmer brake pedal, increasing confidence.
Finally, if after all that you still need more braking power, then you can consider a BBK upgrade. Don't waste time and money importing a newer set of GT brakes - just go Brembo or similar. I personally upgraded my 2.5i's brakes to Brembo's (from a wrecked MY02 Impreza WRX STi in NZ) , braided lines, STi MBC and BB (from a wrecked MY05 WRX STi), Dot4 fluid, DBA HD discs and Hawke Ceramic pads, and my braking performance has improved substantially (the 2.5i's brakes are smaller than your GT's factory brakes of course, so the difference was a bit larger for me). My setup would require some minor changes to pads and tyres to be effective to abuse on the track, but for street, my setup is near-perfect for cold and hot braking.
I was going to procrastinate, but I put it off...