In the case of a nitrous or blower deal I believe bigger is better. FWIW it of course is all combo dependent for sure but in your case I would likely look at the larger tubing size. Also high RPM stuff seems to like a bit more header provided its not a very small cube deal. We went from an 1 7/8" to 2" header on the Vette a few years ago to a 2 1/8 2 /14 2 3/8" deal on the Vette and found 28HP. In that world thats huge but we knew we had grown well past the small tubes. We have pipemax as well, but couple that with our experiences to make a final decisionon tubing size. BTW the large tube headers that were on our dragster were from when the engine was a nitrous piece trying to run TD.