bigger question is why was the cat converter choked in the first place?
thats why I asked for fuel trims.
fuel trims can tell you a lot.
cat choking is not normal, the cat operates at very high temperatures and unless its poisoned by coolant, silicone, lead, zinc etc. it wont clog or lose performance.
The rear o2 sensor can tell you a lot for this problem.
btw - I just repaired a car with a case of extreme knock, even on 93 octane fuel, the fuel trims were the smoking gun in the diagnosis.
it had a stuck and dirty EGR along with an air leak after the MAF.
after the cleanup - no more knock and smooth as double cream