I think we're coming at it from different angles.
My point was that on a bunch of images whose quality you are happy with, for example images straight out of a scanner/camera, you pass them through JPEGmini and its automatic process keeps the quality the same, and reduces the filesize dramatically.
Of course you can manually try to match its results, by tuning photoshop export, but that's missing the point. By doing that you're just resetting the baseline of a start image you are happy with. Then you would run JPEGmini on that to get the same visual quality at a lower filesize, much less than 8MB.
Hopefully that makes sense.
Otherwise... we can agree to disagree on this.