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Of course you can fool around but chances are it's the cat. They're only guaranteed for 50K (now up to 80) so 360K is a real good run.
There are tests you can do, like check the oxygen reserve before and after the cat, but now is probably the time to replace the cat.
A simple google search yields:
Catalytic converters can be checked in two ways. Temperature, the temperature of the outlet should be approximately one hundred degrees higher than at the inlet Emission levels; run the engine slowly up to 2500 rpm, hold steady while monitoring the 02 level, when the 02 level has bottomed out at it's lowest level (less than 1% with air management disabled) sharply tag the throttle. After the "snap throttle" bring the rpm slowly back to idle, the 02 level should rise and then come down.
(You can check the O2 level by reading the 02 sensor voltage).
Lastly, my experience with a 260K saab OEM converter was similar to yours...everything else was ok except high NOx. New cat fixed the NOx problem AND lowered the HC and CO levels to about 1/10 of what they were before (even though the car passed the HC and CO levels.
FWIW, the emissions test levels aren't going to get any higher...they keep lowering the pass levels at inspection every year even though the levels will probably never be as low as the car had to pass when it was new. The upshot is you'll probably fail your HC or CO emissions next time unless you replace the cat.
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