OK, so here'* where I'll pipe in...
My White Horse has over 182,000 on it and still has the original CAT. Both my O2 sensors are working and register proper readings when scanned (these have been replaced). Car runs great...as smooth as silk as usual.
My point is that time and miles should not be the only criteria used to determine whether the catalytic converter needs replacing. Only replace as it truly needs replacing. That is to say, when proper diagnostic procedures show that it needs replacing.
Of course, I haven't been around much lately, so it may be that you've already done so. In which case.....Never Mind!
Mike: 1997 SE w/ 183K, aka White Horse
, Gutted Airbox w/K&N, drilled 180* t-stat, tint all around, clear corners w/SilverStars, "PONTIAC" light up tail, PEMs, NGK TR55s