You have a 2010 WRX? THEN DON'T BOTHER WITH SS LINES YET. Your brake lines are too new to have much flex.
I replaced my lines at around 20k miles and there was hardly any improvement because my lines were not "old".
You should look into new pads (less compressible) and a master cylinder brace. (the GD chassis has a flexy fire wall, so I'm guessing the GR does too, albeit not as as bad)