My cousin in M'ville, what's up?
I have thought about it a little and tried to find more info, but google is letting me down on this subject.
The main concern with gutting the cats is that it will create a large open chamber in the emptied out cat shell. This large chamber allows the exhaust gasses to slow down once it enters the chamber, and must be accelerated again when it exits the chamber. The theory is that it will be more efficient to have exhaust tubes of constant effective diameter. This is the theory I could find, not sure if I buy it or not though.
I would like to see some dyno results of with gutted cats; before and after of course.
Since your cats are obviously in good condition I would suggest not destroying them. If nothing else remove them and install an aftermarket off-road H-pipe. Then the next time you do have to pass emissions, you will have a good set of cats to throw on the car.
ebay should have some used offroad pipes fairly cheap.
jason