JIM, i think you mean bib-mousse, they arent new michelin had them out for years , we have used them mainly on enduro bikes, only thing is the pressure is fixed so you buy one pressure and thats it, it like a foam donut that replaces the tube, i have one on my YZF front as we speak, im not sure how they would go on flat track , they are for more an upright profile.
Rosco most guys on our dolomite run between 8 -15, depending on if they want grip or slip, i find if im not getting angles or coming in dead, a few more psi and the back end seems to want to flow rather then bog. i think it depends on your style and you bikes turn in and drive out, what ever works is you PSi on the day