On the right combo they make a pretty big difference. They have been shown to gain more on a stock LS1 with an intake manifold swap only compared to similar 1 3/4" headers. That being said for a daily driven bolt on mod only 5.7 or 6.0 I would still probably go with a 1 3/4" header as the low RPM power and part throttle power would be that much better, and the top end wouldnt be THAT different.

You start doing mods like a cam then its a different ball game, especially with the LS2 that comes with the better flowing 243 heads. If you plan to do aftermarket heads along with a cam and intake I would step up to the 1 7/8" headers pretty much every time, especially with the 6.0.

 

Great! So im right on the money for what im wanting to accomplish in the long run.