[guye]

I just ceramic coated my cats. Engine is heaps cooler. Cats are meant to reach effective temp quicker.

Yes the cats are restrictive. Generally, higher euro number = more restrictive, as denser cells per square inch (in order to get more sacrificial material surface area inside the cat).

They do make the exhaust a bit quieter. But the cat on its own would be insufficient to make it quiet enough for a rego pass in most cases. I needed the cat and 2 mufflers (each side) on my full length undercar system to keep the noise low enough for a pass. That's the stationary 90db test at 75% revs.