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

I was running 1 5/8" street type headers with extensions on my 408 & I changed to 1 7/8" race headers with long collectors. I saw a small change in ET & MPH to the good. I didn't get a chance to really wring out the 408, I'm in the process of building a 416 because I dropped a valve in the 408, I guess we will see if there is any improvement with the 416.