Glad to hear you passed, maybe your cats aren't too bad, not sure. The temperature difference still is a concern but you may be ok for a bit. The honeycomb can break down even more and cause much more back pressure, you will notice it if/when it happens.
But in my opinion, regardless if you passed, I would be looking into replacement cats or a different header. Keep an eye on the temperatures, you can get a temp IR gun at Harbor Freight for like $20. Since the CEL won't tell you how bad the cats get, your only indicator now will be lack of performance, poor acceleration, sounds muffled, etc. I only say this because I've heard of it happen a number of times, some that have used a sim as well. High back pressure really puts a strain on the whole engine.
'02 IS300 MSM LSD