I have the first Top Speed headers and Exhaust to be imported into the US (test car for the product by importer, Che in Dallas).
I am running factory cats on the 97, which is just one set.
The combination is loud. I've heard louder, but I've also heard a lot quieter too. It's excellent for track use because you can hear your motor with the windows down and a helmet on and you know when to upshift.
Since today's Friday and I'll probably leave the office early and won't sit in too much traffic, I took the boxster to work this morning. Going through the parking garage, you'd think there was some sort of sport bike flying down the ramps. I set off alarms and turn every head that I drive near, even if they're in their cars on the other side.
The combination is loud. Did I forget to mention that?
BTW, there's cabin drone at 2-3k rpm. Brace yourself.