Tough to get. I had an 08 wrx (different then yours obviously) and stock to stage 1 was mostly a drivabilty improvement. While is added some boost and made the taper hold boost longer, it really made the throttle and torque table smooth. I'd guess it'd made maybe a few tenths on a 1/4 run. Stage 2 on the the other hand bumps up the hp quite a bit over stock. I just don't have any real numbers for you on drag times.
AEM CAI, Perrin ELH wrapped, Catted Downpipe, Stage II XPT tune, K4RT30Y STS, lip, shark fin