I ran an oem cat back on track, with a Buddyclub manifold, so still no cat.
It certainly robbed power, noticeably so. Vtec didn't pull as hard, and took longer to start pulling.
That said, its mapped to a Buddyclub spec 3 and made a lot more than standard. So I assume that's why. And it wasn't just the noise making it seem slower. I ran it for a week.
Noise wise...
Mine, buddyclub header oem cat back was 94db I think.
Buddyclub system was 110db.
Another teg with dc sports header and spoon n cat back was 104db.