print them as high as your printer will go. you dont use any more ink by printing at higher res. why not just try it and see if its ok?
600 dpi is the highest my printer will go. I'm asking if that is a good resolution to print photos - will they be clear or will they lose some of their quality?
i cant understand why you dont just try it and see for yourself. Depending on the resolution of the original it may be as good or may be worse. If it is a colour laser printer 600dpi will give a decent result. For an inkjet though 600dpi will look pretty bad.