From what I've seen on the flow bench, and measuring the CSA with and without the vane on the floor, it speeds the air up too much unless your keeping the lift below .550 and rpm range (typical 5.7 - 6.4 cid)below 6000.
We've found really good flow and power (5.7 eagle head, 6.1, and 6.4 heads)getting creative with the valve job/bowl/chamber area.

We also measure rev. flow on the intake up to .250 lift and make sure it's in check.
Brian