I have the Epson Photo printer 720x720. I was told by a tech at Epson
that the max resolution in a scan needed to get the best results was 1/3
the output resolution. That being 240dpi. Now with the upcoming 1,440x720
Epson Photo I don't know if you'd get anything out of a higher res. file?
But I'm getting great output on Canon High Gloss Film ($17 for 10 sheets)
Very close to Cibachrome glossy.