Totally agree that velocity is the most important, but here’s the problem with the ‘chase velocity, not cfm’ arguement. There are two primary ways to come up with average velocity through the entire port. The difficult way is with the pitot tube. This requires lots of accurate velocity measurements and lots of accurate area measurements. Not easy to do.
The easy way is to take the port volume (measured with a liquid) and divide it by the port centerline length. This gives the average port cross sectional area. Then you take the cfm reading and divide it by the average CSA. This gives you velocity.
Since velocity is calculated from cfm, the way that you chase velocity is by monitoring cfm.