Your cats should be good for close to 125, 000 miles!
With the two cat system, (pre- and post Cat), they doe a better job with less strain on one unit.
The only thing is they really do bog down the system a bit.
We ripped the OEM muffler off our '03 Safari and replaced it with a 3" Flowtech Afterburner.
Gave it a nice mellow rumble and my wife likes hearing the vehicle running.
Our kids also know when she's coming so they're ready to go!
Even after the muffler change and re-programming the stock computer with the JET unit, my 95 with over 265,000 miles on it will outrun the '03!