The combination of high performance pads in the front and OEM pads in the back can make a very dangerous rear brake bias on the WRX. I'd honestly stick to the same type of pad in the front/rear on as the Impreza seems to touchy with this. You might not notice this until you're in a emergency situation or in a track enviroment.
already ordered new pads for the rear a couple days ago
hawk doesn't make a rear pad tho
i autox my nonWRX subaru
quite frequently so yeah, that's why the better pads. the rear end doesn't get upset at all with the current setup.
yeah, if you don't ever track the car or drive it real hard there's really no point going with bigger calipers unless you want it too look cool. better pads/fluid/stainless steel brake lines oughta work out nicely, i'd go that route if i were you.