I scan negatives and slides at 3200 dpi. That may be a slightly overkill, but I don't feel like undershooting and then needing to go back and rescan them again later. A 3200 dpi scan results in a file that's about 12mp... rather like my D3's. I did an experiment with 6400 dpi and those files are about 45-50mp. They aren't any more usable. The V700 is a little better (I have one of those down at the historical society) but not much.
I recently scanned an old negative at 3200 dpi and was able to produce a reasonable 24x36" print. We have a silver gelatin print of the original negative at the society and I do not think that my print is as good technically. On the other hand, if you put them on the wall, you're unlikely to notice the difference. The original is mounted about six feet off the ground and from the typical viewing distance of maybe 8-10 feet I am confident that digital print would not be viewed substantially differently.
_____ Brian... a bicoastal Nikonian and Team Member
My gallery is online. Comments and critique welcomed any time!