Well, I wish I knew the particulars between the two - Speed(MPH) vs Engine Speed..
All I know is that, between the two, the peak numbers and the curves were quite different - this happened on my last dyno session as I saw the operator switching between the two, while viewing the charts.. I also know that to get Engine Speed charts, you have to hook up a sensor onto the plug wire from the dyno.. And apparently, Speed(MPH) is calc'd off the drum with no extra sensor needed..

One thing is for sure - you have to be using the same gear (4th in my case) and the same settings for the charts - to get comparable data..

 

You are certainly correct about area under the curves being more important than the peak numbers.. But knowing that and understanding that are two separate issues..lol It's hard to analyze areas under curves and easy to look at the peak numbers.. Still, I fall prey to "Bubbas' armchair analysis" syndrome every now and then..lol