mechanic mate replaced one (exhaust not sure if new cat) last week i think (on EF falcon)
i was hanging around (i actually help them a bit so his boss likes me) and as far as i can recall they did not have a sensor after the cat so it should not hurt. if you are not sure just look under the car
and with no cat you have less back pressure which should mean slightly better performance/economy
and for those people goin oooo bad fumes, piss off even new diesels spew out much worse stuff, all those micro particles from the diesels are absorbed through your lungs and go through your whole body(in the US they are really starting to worry about this especially in California), yet people are espousing the value of diesel power vehicles in city/suburban environments with lots of people around
and it isn't even economic for most soccer mums anyway as they would have to be doing 30 000km a year and keep them for 9 or 10 years to break even with fuel at $1.50
and if its a stocker running low octane(normal) fuel there will be fuck all cyclic alkanes/kenes (the bad ones) getting thorugh combustion anyway as there is fuck all in the fuel to start with.
obviously you would want to bash out and leave the old cat body so you could say it must have died after you got the new rear section, i don't think many cops/epa people would try and do you for it unless it was very sus(thats why you leave dead cat on there instead of straight pipe), and it isn't as if you have a high chance of anyone looking anyway. The cat on my mums ~94 magna died recently (buzz buzz buzz) and there is no way we are gonna pay for another one unless the body of the cat rusts through (unlikely)