That is an interesting question and one that I don't think has ever really been tested beyond the calibrated seat of the pants tests. Personally, I've not noticed a difference that I could actually feel.
Here are some pictures of the production cast aluminum manifolds and some of the support brackets making their way into the machine shop. Also you can see some of the billet aluminum end tanks in the mill going through their first op.
The machining of the intake manifold is an 8 operation process. The mounting bracket is a piece of billet aluminum which is waterjet cut then comes back to the machine shop for drilling and tapping and finishing. The end tanks are also billet aluminum and are only a two operation process but the machine marks left behind in the aluminum are beautiful and really make the intercooler pop!
Manifolds:
Support Bracket:
Intercooler end tank:
