This isn’t proven fact, just anecdotal, but it seems that since Subaru introduced Electronic Brakeforce Distribution (EBD) in 2002 (which controls the rear brakes independently instead of one and prevents the car from twists and makes unwanted turns under hard braking), seems to be the cause of the rear pads wearing faster than the front ones. I’ve never seen the rear wear out so quickly in any Subaru I’ve owned before. It’s not a big deal though, it’s good to see they’re getting used to it.
Used to run Hawk Ceramic pads on my previous STi’s and then my Brembo upgraded Liberty for a long time, later switched to QFM HPX. The QFM HPX pads were very good when cold and great when hot – even in track conditions there was virtually no fade in them after a day of wiping them, with the only downside being a little dustier than the Hawk .