I experiment with headers and pipes a pretty good bit and for me on my MP9TKI4 with a NR Rolling engine,

I think the 9853 pipe used with the 41031 header is the best combination. It gives a combination of strong low end with great top end. Of course all this is at the expense of gas mileage. I haven't checked run time lately but it was getting around 10 minutes the last time I checked it.

Lee