There's a very easy way to test for clogged cats
remove o2 sensors- install bung / low pressure gauge. anything over about 2psi - you're clogged up.
cats clog for a reason- there's an underlying issue.
here's a link for setup and procedure : http://www.meurosport.com/Cat_Testing.php
I know the person who designed / tested this setup from online forums-- reputable source.
It's not what you buy, it's what you build- Unknown
EN90283 - Stabled for HG repair
DH06247 - Running like a champ