I finally got around to test the three typical manifolds on my setup and doing virtual dyno runs. GTiR and Avenir mani's made about the same power, with Avenir doing slightly better. I tested them against a tubular ASP VET manifold, the gains where very minimal, under 10whp. Granted this was on a low overlap Roller Rocker head with RR cams (Stock DE's have similar overlap numbers though, thus would have very similar numbers).
Moral of the story, stick with GTiR or Avenir manifolds for stock camed setups.