It's an '06, so it has the 2.5L. '05 was the year they put the 2.0L in the Aero and WRX.
I have to admit I like the body on the Saab better than the WRX, but I like the interior better on the Subaru. My Cousin owns an '06 Aero, and my buddy has the non-turbo version 9-2x Linear, but with a full STi drivetrain and brake swap.
Like these guys have said, go to Subaru for anything other than body panels or interior. And, I wouldn't doubt if the Subaru interior would be cheaper if you needed to replace anything, due to the limited run of the Saab version.