Bad Catalytic Converter, Driving - Good or Bad Idea? Options

[JoKeRkId613]

So I'm throwing a CEL which, according to the dealer, is "catalyst efficiency below threshold". The mechanic told me the catalytic converter is bad and they're getting me a new one under warranty. Great. They told me I can drive the car around normally without a problem for the next week or two while I the part comes in... How safe am I really? I was racing a Civic Si turbo at the track the other day and after I beat him, he goes to me - "hey, you should tune your car, it's running very rich". My car is tuned, though. And I'm sure the reason he said that was because I was blowing out what looked like white smoke through my rear view mirror from my exhaust. And I've noticed I've been getting crappy gas mileage since I got the CEL.

Is it bad to drive around with a bad cat? if so, why?

Thanks guys.

[JoKeRkId613]

That's what I thought. I'm harming the environment. Would there be any damages to my motor though? I friend of mine told me to be easy on the car and not run it hard while I'm waiting for the new cat.