A few years ago Mopar Muscle magazine had a coronet convertible project car with a 440 (If I remember correctly?) Anyhow, they did a comparison with stock vs. extrude honed manifolds and it only resulted in a small performance gain. They then went to headers and got a pretty good performance gain. Sorry, I don't recall the exact numbers. I would only do the extrude hone route if you have to use the stock manifolds.
