Theres another new choice which is only fairly recent. Its based on the Vn Grp A setup and is made by a mob called Trickshift.
they tested it on a stock 5ltr with a 185 chip, and had approx a 20% gain... they are testing a 355 mule in a few weeks aswell. they have compared it to other manifolds, and hp figures were not far off the likes of group a, but there manifold had greater midrange torque.
The manifold runners themselves have been ported in areas to make flow consitant the length of the runner. At the top of the runners is a 2 part plenum, and the base part of the plenum has bellmouths leading into the ports to assist airflow. It has been in development for 2 years and the throttle bodies are twin V6 for 5litre, and one V6 and one V8 for a 355 application.
The rear throttle body is on a 30% delay, but opens faster so both throttle bodies reach WOT at the same time. At this time they have no plans for a drivers side outlet, as the tooling for such a cast change is rather expensive, and not feasible at this point. They made it as stock as possible and bolts straight on , the only mod you need to do is shorten the kickdown cable. It fits directly under the bonnet with extra room aswell so no bonnet bulge is required , it provide easy dizzy access (not like the hidden one on standards 5lt donks) and it also runs of the factory comp and no tuning will be required.
Price seems to be around $1800 - $2000
*Info from another post from another forum