I'm not sure about GPs but among the V6 Fbody guys there's been a debate for years over if the Holden or Fbody 3800 intake manifolds is better than the other. A shop wot-tech are doing comparisons stock for stock right now and eventually modified setups. I know a couple of people here have run either setup and figured it would be a good tech article to share.
http://wot-tech.com/shop/gm-3800-v6/...s/cat_145.html
Right now the fbody intake is better than the Holden in the complete setup. A lower Holden is much better though. Some people are starting to fan a different upper for the Holden and are getting good numbers with them.