Digital BW, The Print

I too scan my 4x5s at 1600 dpi using an Epson 3200.  If you assume you send
to the printer driver at 360 dpi, a 1600 dpi scan will let you print up to
about 16x20 depending on whether you do any cropping or not.  There is
really no need to send to the printer at 600 dpi.  Using the Epson drivers,
300 or more is good enough and if you are using Qimage, I am confident you
could print much larger (with lower effective dpi) and get good results.

I did some initial scans at 3200 dpi and didn't have problems with the files
in Photoshop, but I did find that Qimage had problems with the file sizes
associated with a 3200 dpi scan.  No problems with Qimage and the 1600 dpi
scan.  My output right now is limited to 13x19 because my printer is an
Epson 2200, but I am confident with my 1600 dpi scans, I can pretty much
print any size I want.

Also by the way, I scan in 16 bit grayscale to keep file sizes reasonable.

Paul