Scanning the 4x5 at 5000 ppi changes the relative equations quite a bit. However the limitations of the large format lens / negative combo still limit the image resolution to about 40 lpi and with great lenses, perhaps 60 lpi. The 5000 ppi scan will then be recording the grain structure but you won't be getting additional image sharpness because of it.
But I really meant lines per millimeter not lines per inch.
Mea Culpa - old age makes it difficult to distinguish between inches and millimeters <grin>
