Martin
360 dpi is optimal for sharp printing of text and
slopy thin lines on Epson printers (they use
360-720-1440-2880 dpi as printing resolution). But 180
dpi is good too, there are differences but visible
only side by side from very short distance.
For HP/Canon and others printers using
300-600-1200-2400 dpi for printing is 300 dpi the
optimal, but 150 good too.
The choice of resolution depends on scale between
size of map and final size of print. If you should
downsize your map to print there is optimal
resolution of rasterising not necessary.
Martin