with the layout software, does that get me three across or am I still leaving swaths of unused paper?
The one's I quoted all use the driver so the same limitations apply. Potentially a RIP could solve your problems but I'd hate to see you go that route. Again a different roll would be far more elegant.
I'm open to suggestions on 10" rolls. I have the Kodak and find it to be ok, but not nearly as nice as the Moab.
Canon and Epson both sell excellent 10" rolls of luster/satin last time I checked.