Coming from someone who owns both. A stg2 WRX will never walk a stock GTO (ls1 or ls2). A stock STi is a good race from the line, but if drivers are equal, the goat should win.
GTO myth number 1: The 5.7s are slower than the 6.0s... depends. I know of few not modded.
A stg2 STi should run with or beat a stock goat.
BUT! Here's the big butt... show me a stock WRX, STi, or GTO at the track.
BTW, I smoked a 350Z in my stg2 WRX last week, but it was stock and a convert.