if your cat is really plugged, your engine will actually start pinging. Mine started with the common pinging culprits like leaky injector seals/buildup in upper and lower IM. Then I started having CEL, so my guess is the pinging caused the engine to run really rich which caused my cats to meltdown. Anyhow I digress, with the cats plugged your top end should feal really slugish. With mine I still had a LOT of intake noise though, so it sounded like it was going fast but really wasn't. I ended up just bringing mine to a dealer and they gutted the cats for me, after that all was better.
BTW sorry for the long post
