[maxerickson]

Catalytic converters are not really impacting performance most of the time, at least in terms of power. There are some efficiency losses from the restriction, but the net result is much cleaner exhaust. At peak power there is some reduction due to the converter, but it has been completely swamped by improvements in power density, so it isn't something anybody should be worried about. If you aren't running at peak power, the losses don't really matter.