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).
In reply to Simon4:
for 5 - a 60m rope would work well as it gives a bit omre of a gap - 12m eahc (less knots) - Beal Joker? 9mm, full rope. Good for cragging etc too.
As others have said it is a minor issue between 5 but carrying to/from would be onerous - split other kit (aves, 'pons etc) though and it ought to work out fine.
In reply to marmot hunter: Never quite seen the appeal of 60m for cragging, the extra 10 m will almost entirely be a nuiscance and heavier, while I have yet to find that 50m is not enough for UK cragging.
If I were in the OP's position and thinking about cragging use afterwards, I might buy a 50m Beal Cobra (not in theory a single rope, but would do fine for glacier travel). But then I did climb the Dent d'Herrens with 30m of 8mm walker's confidence rope!
In reply to Big Lee: If you are suitably spaced, no-one should go any great distance into a crevasse, hopefully no more than waist-deep at the most. I can't see why there should be any more faff, while the 2 would certainly be more exposed on their own.
For pure glacier travel, I would far rather be on a rope of 5 than a rope of 2.
In reply to Laurence Dowell: I'd agree with the others that you'd need at least 50m and would suggest either a Beal Iceline 8.1mm or a Mammut Phoenix 8mm. Both are dry treated and both are excellent half ropes that you can use for rock, ice and alpine climbing.
Personally, I am quite happy travelling on a glacier with one half rope. If, however, you want the reassurance of a single rope then the Mammut Serenity 8.9mm is also dry treated and is the thinnest single rope available.