I am aware this is an old thread but the war with the EPA is really picking up steam and I figure this should be an always open/ evolving topic. Catalytic converters are now on all petro burning motors. Even weedeaters! Funny thing is that cats actually cause a piston driven motor to work harder resulting in more fossil fuels being burnt.
On any given automobile platform, eliminating catalytic converters can actually reduce fuel consumption by 4 miles per gallon. With EMS systems and head designs, there is almost a "complete" burn of each combustion cycle. So, as you see we really are going green. But what green is the actual question.
Don`t ask me, I only own a shop and do this for a living.