I have an SPT (Borla) exhaust on my '11 STi. The exhaust is loud, even at idle, and while driving, it is loud enough to set off car alarms when driving down a side street or in a parking garage. I would prefer if it were quieter, but I like the rumble. The down pipe is the stock 2.5 inch catted pipe, and the cat-back is 3 inches, but replacing the downpipe with a three inch pipe would only add a couple of WHP. If I wanted to be even more obnoxious (I have four Hellas up front), I would have installed an external waste gate.
I have an Invidia N1 on my '02 bugeye. The N1 is quieter at idle but gets loud in the power-band under throttle. Different motor, but the N1 has a much different sound; more whine, less rumble.
I am in Watertown.
(Trust Max on the rust issue. My '11 has been fine, but he sees a lot of Subarus every day.)