In reply to Laurence Dowell: Pure glacier travel, with nothing like moving along an Alpine ridge, or any more technical bits?
Well you wouldn't want less than 50m, so you could be (roughly, obviously the knots take up some rope), 10 m apart.
But why would you worry excessively about getting the lightest and shortest rope possible? That matters a lot for a party of 2, but diluted among 5? Any 9mm or 10mm should do the trick, you could go to a smaller diameter if you wanted, but why bother (apart from the fact that the rope has to be carried by one person when NOT on the glacier).