I have an Epson 1640 SU also and I use it for a digital darkroom when I'm doing color negs to prints and it seems to do a pretty good job. It will do 9600 dpi optical and a few steps beyond interpolated so I can do a decent job on 35mm film. Still doesn't compare to a silver print though!
BTW because of the newer models coming out the prices on these have plummeted where you can find them.