The 60 micro would be the perfect choice for reproducing documents I think. It's as sharp as any nikkor ever made, right across the field (Unlike the 105 micro say, which is a tiny bit softer in the corners when wide open. I don't know what the Sigma is like in that respect never having used one.)
The 60 is also a cracking short tele (on a DSLR) used anywhere in close to medium range, although it's so ferociously sharp you might not be thanked much by anyone whose portrait you took with it. It's a superb flower lens for example, although I prefer the new 105 VR micro for that, many people would rather have the 60 because it's possibly a bit sharper (I can't tell the difference but I've seen test charts that say there is one), lighter and so much more compact.
You can generally find the 60 pretty cheap in mint condition somewhere like Aperture, Ffordes or Grays. There seem to be a lot of them about at the moment, perhaps because people are selling them to buy the 105 VR.
If you can find one, the rare AF version of the 55 micro might be an even better choice, because it reputedly (I've never even seen one in person) performs equally well up close, but maintains that performance out to infinity, whereas the some people say the 60 isn't quite as good to infinity as it is close up (it seemed fine to me though)
I'm assuming that you don't want to be mucking about with the various MF 55 versions (which are very good bargains and readily available) if you're using a D50 because they won't meter. (Although they will on a D200)
If money is no object though, I'd be awfully tempted to go for the 105 VR and stop it down a bit to get the corners dead sharp for your copying job. It's an incredibly flexible lens with superb colour reproduction and contrast, probably just as sharp as the 60 in the centre and very close in the corners when it's stopped down to about f5.6 - f8. Used wide open it perhaps isn't quite as sharp (although there's not much in it that you can see in any normal situation) but it produces really dreamy-looking half-melted backgrounds which I find very appealing and which are far nicer than the ones you'd get using the 60. It's a bit of a bazooka in size (about the same as a 17-55 say) especially with the hood, but the VR makes it very useful as a general purpose moderate length telephoto hand-held and still works fairly well even when you're doing stuff like flower or butterfly pictures around 1:3 - 1:4. You'd turn that function off and use a tripod or copy stand for serious macro though because it doesn't really do anything to help once you're down past about 1:2.
I should make a disclaimer here though because I got one a couple of months ago and I'm in love with it. I've hardly had the thing off my camera since acquiring it
