Not sure really, maybe in their testing .jpg was significantly quicker. Actually, if you expand the 'Load Mesh' option in the previewer you can manually import images, so if you're desperate to check something now you can export like usual (except gloss separate from spec) then do that. One button is 'load map from active…
That worn edges is probably from the cavity map that's generated from the normal or inputted at the beginning. That'll be one of the top layer in the group (spec and diffuse), below the AO layer. The other stuff I have no idea about. Maybe you should elaborate more on what you mean by edit the 'default materials' — do you…