I should add that since that test, I now find the foam to be useless in anything less than 3000. 3M did it right with the choice on what grit to add the foam backing for their trizact system (which I no longer use).
The reason I say it's useless courser than 3000 is because regular paper on a hard pad or rubber sanding block levels much better than something with give to it like a foam pad. Also, the regular wet/dry paper is cheap and the foams are very EXPENSIVE as in $3-$6 per disc.
I now use:
-Abranet P600 dry (lasts as long as probably 20 pieces of wet/dry)
-P800 - P2500 wet/dry in steps
-3000 or 4000 grit Foam pad (Abranet, or similar) and this is when I have it around.
I also tested only using the Dynabrade at 4000 (sanding with the N.D. or by hand on all courser grits) and I still found a few pigtails after buffing when I looked hard and that was at 4000. That settled it for me.