Well, I am not sure which is more restrictive... factory catted h-pipe or crimped factory headers. Either way, getting rid of that stock h-pipe was one of my favorite upgrades yet... it made my exhaust sound AWESOME!! I would definitely get that stock one off there if that's what you are asking this question for, you won't regret it.
I upgraded to an X pipe with 2 high flow cats and it was way better than the stock H pipe with 4 cats. The stock cats are extremely restrictive. After the upgrade, I could tell a power difference, volume increase, and quicker acceleration through the rpms.
If I started over again, the X pipe would be my first mod and then subs and so on.