I thought the stock Impreza was a little squirly at 90 plus. It seemed to drift to me if I remember correctly.
I switched to Yoko A520 (not recomended) whiteline adj rear sway bar (set at 20mm) the Rallispec STI V5 struts with progressive eibachs (rear progresive) (highly recomended) and the car is 100% better. I drive a fast everyday and the setup instills confidence.
For example a long sweeper that I used to push at 80 stock can now easily be navigated at 100. I dont have the b#$%^ to go faster in fear of jail if i get caught.
Well I love my impreza put out for a bar to start with then look at suspension options. My rallispec setup is now selling for 750 i paid 1050. It was a good deal at 1050.