hey, i think you were really lucky to get away with the no cat fine! i heard it was much more than 5k!!! anyways, a catalytic convertor is a massive restriction in your exhaust system, its not .5 of a kw, try 10+ !!!
as i know it, with an aftermarket ecu or any modification that alters the induction or exhaust emissions of a car is deemed unroadworthy unless it meets standard epa regulations - this means air pod, exhaust, bov, ecu etc.
all they are trying to do is keep environmental pollution to a minimum and save this dying earth.....