There are so many variables with GC setups, you could have anything between awful to awesome. This is because you can choose that shocks to put them on, what spring rates and lengths to put at each corner, and what height to run at each corner.

I had 300 lb/in front, 250 lb/in rear, 8" springs on KYB AGX on my GC8 sedan and it cornered like it was on rails and was very well damped, although with AGX's, well damped also means very stiff, but liveable in NYC (unless you have to go to the bathroom).

I liked that setup a bit better than the JIC FLTA2's I had on my WRX wagon, as that was too uncompliant for anything besides track days.

For a rallyx setup, I'd recommend 9" springs, as that will let you go a little below and a little above stock ride height. Something around the 200 lb/in range should work nicely too, and I'll leave it up to you to determine the front/rear split.