The mopar performance one is not a replacement one for the original. It is a copy of the cast Ray barton one as far as flow. They do make more power than an original but there is usually a drivability problem for the street.
I have made as much as 980hp with one and I know you cant make that with a stock one. Also since the lids come off you can get in there and do some modifying to them aspecially with cross over and plenum. There is the problem with the height tho.