I apologize for my ignorance, but what is a mobile dimension sawmill? Can you provide a link to a vendor, maybe the vendor you're most interested in?
I watched their video here http://www.mobilemfg.com/portable-saw-videos.html
Looks like an interesting saw, but I don't have an memory of seeing one operate or hearing about. Dean's suggestion to visit the forestry forum would take you into a section that talks only about portable mills...someone there must have experience.