One more thing about the difference between my 2010 WRX and my new 2013 STI. The stock exhaust on the new STI sounds aftermarket. I don't know if the 2011/2012 WRX/STI exhausts are the same, but this sounds great.
I rolled up to a meet a few weeks ago and the guys there were asking what exhaust I had. I explained it was bone stock, they were pretty surprised. My neighbors and wife hear me coming through the neighborhood before they ever see the car coming. Again, maybe all 2011+ WRX/STI's sound like this, but I've been around a few and didn't notice their exhaust sounding so "deep." I feel no need for an aftermarket cat-back, I love the stock exhaust sound.