Ckw From UK - England, joined Aug 2010, 795 posts, RR: 15
Reply 1, posted (12 years 9 months 2 weeks 10 hours ago) and read 1520 times:
If you mean how much useful info there is in a 6x4 print, there are too many variables to give a simple answer - depends on sharpness, finish, graininess etc.
A more practical answer is that the scanners you mention are easily capable of extracting all the useful info from a typical colour print.
The figure 300dpi is a useful benchmark in so far as it is the resolution usually required for quality magazine printing. BUT just because your scanner is capable of this resolution, the quality you get will depend on the quality of the originals - no scanner can make up for missing detail or sharpness.