Holden Performance - Holden exhaust manifolds?

I'm looking through my LS1 installation guide and they show Holden exhaust manifolds which look different than the LS1 ones,are there any performance gains by using these?

I wouldn't think you would find anything measurable.

These look different than the US manifolds and look like I would get the clearance I need on my LS6,I'm concerned if the LS1's and the LS6'S flow the same.