For the V6's an improvement is less likely. The V8's still have four, so removing one and using a better version for the other will help.
FYI, if you can, get a look at the outlet side of a cat housing, inside. The brick inside creates a very large slow moving exhaust flow. That exhaust is then forced to hit a blockage(outer shell of cat), and collide into a small round opening. Notice that I did not use the term "funnel" to describe that transition.
The transition on the outlet side of all catalytic converters is awful. Note that I include all high flow cats in that statement. The outlet of a cat should be shaped like the outlet of a header collector. The large size(area) of the brick should be transitioned smoothly down to the appropriate sized pipe, with no protrusions, weld slag, etc.
If you want an improvement, have the outlet side of the cats cut off, and replace them with a collector adapter, Buy the adapters that transition 3.5" collectors down to 2.5" pipe, etc. Trim them to fit, whatever it takes, and you will gain free horsepower. Regards,