The biggest thing I learned after getting into national competition with my G-stock 2.5RS (and running an STS prepped 2.5RS quite a bit) and a BS Porsche Boxster, is that different mods will effect the car at different points of the corner. There are really three stages to a corner, corner entry, mid corner, and corner exit.
Rear toe-out on the Subie will aid with the balance of the car throughout the corner, but has the best effect on helping the car to rotate (or better put, not push on throttle) coming off the corner. It helps to get the car to drive like a rear driver coming out of corners.
More rear bar can be used to help the Subie to get the mid corner balance where yo want it, especially useful on NT courses with lots of sweepers.
Way low or way high rear tire pressure can help with getting a Subie loose on corner entry.
What is interesting (and obvious, but not to me at the time, because my experience level was all FWD and AWD) is that these same mods on the Boxster could have different effects, because we were more traction limited. We had corner entry and mid corner balance just right, but without some toe-in at the rear, it had trouble getting loose on throttle coming off corners. upping the rear pressures a couple pounds helped the car to keep the ass inline better, but then it was too much pressure for getting power down to the ground.
Again, changing toe, or pressures, or roll stiffness can effect the car at different point on a corner, and the layout of the car will be different too. Lots of experience helps to figure it all out.
BTW...i learned all about the rear toe-out trick from Brian Priebe about 4 years ago, who had experimented with it on his STS Subie the year before. Once the secret was out, rear toe-out has become a standard for Subies in autocross.