1 3/4" Headers Verses 1 7/8" on a Healthy 408....Is There a Big Difference??

I've got some money burning a hole in my pocket, and I'm wondering if it would make any real difference swapping from my current 1 3/4" Headman Hustlers to the 1 7/8" Headman Hustlers. I think my engine is right on the boarder of "needing" 1 7/8" headers, but I'm not sure if I would gain much (if any) with the swap.

My car, incase you are not familiar:

67 Barracuda (about 3250# with me), 408 stroker, 13:1 compression on e85, ported Edelbrocks, 264/268 duration @ 0.05 with 0.621/0.632 lift solid flat tappet, Victor intake, 727 with 8" converter, 4.10 gear, 275/60/r15 Hooiser DR.

Current best 10.1x @ 130mph, but usually runs 10.3x in the summer heat.

I would just hate to spend the time and money on new headers if they don't to squat....or slow the car down.

Thoughts?