Thought I might share the way my car sounds now that I've finalized the installation. I'm using 2 1/2" pipe from header back with no cat and a Magnaflow SS muffler. It's loud but not obnoxious and, with a cat, would likely be a bit softer.
Just the exhaust in the shop:
https://youtu.be/moxxhgzyYBQ At the track:
https://youtu.be/PxWiI3HWW4M The car is modified with a ECU upgrade by Midnight Tuning and some other small changes; it runs well, I think. Speed is limited at present due to a 3.73 gear (E30 325 diff) so I'm topping out between 115-120 mph with 245/45-17 rear tires.
Exhaust on track-only 318ti 
Hybrid Mode
