i think i'm going to get this exhaust...
Audi B7 A4 Quattro 2.0T > Exhaust > Performance > ES#2225882 Cat-Back Exhaust System - 2.5" Fully Polished - FPIM-0504

i like it because it's apparently the only true cat-back for the B7 A4 2.0T quattro tiptronic. the other makes use the stock downpipe. this kit includes a 2.5" downpipe.

i already have a test pipe and APR stage 2. do you think this exhaust will provide much more power, given the bigger diameter pipes? would it be worth the money, given the expected HP gain?

 

Billy Boat is a reputable name in the VW community. If you already have the test pipe and stage 2, you will not see huge differences. It will mostly be sound only with a tad more power. Personally not worth it to me. The stock pipe is roughly 2.4 inch or 60 ish mm which is why we always say you don't need a full exhaust. I just re-measured from a piece of pipe I had in my garage.