1 7/8 or 1 3/4 headers?

I need new headers when I install the 408 in my 73 Dart Sport. I had the 1 3/4 tti picked out but I see they also have the 1 7/8 as well. I always thought it is better to breathe as well as possible and am thinking of the 1 7/8. It is rated for 550hp and up and I am in the 500hp range. What do you think? I believe bigger is better in this case.