Today's high flow cats hardly impact performance at all, and even factory cats aren't bad these days. I myself usually leave those on nowadays, I hate being behind a car who's exhaust is so offensive I can't have my windows cracked.
And I swear I've been behind a car or two that has actually made my fuel trims start compensating for the cars exhaust that's in front of me.
I've had older style pellet cats and I 100% agree.
For some reason, the old rule that a cat robs a ton of power still lives on 20+ years later. Wasn't there a recent test that proved that two cats inline robbed no more than 3 HP on most cars? Removing it isn't worth the possibility of a huge federal fine in my opinion. Some say their state doesn't do emissions testing but this doesn't mean you're except from a federal law. You get caught and you'll be sorry, all it takes is someone in a bad mood.
I removed the muffler on my 1992 C2500HD pickup and left the pellet style cat. After that I replaced it with a high flow honeycomb cat and a Flowmaster 40 and it was easily two to three as loud as the pellet cat alone. All 3" piping.
Modern cats are absolutely nothing like the ones they had in the 1970s-1980s. Even 2 or 3 in series isn't even close to as restrictive as a single pellet cat, especially after it's been in use for a while.
