In reply to Jonny2vests:
> If you have 60m halves, then you can do most routes on grit with one folded in half.
Indeed, and a "skinny" single is perfect for this. Even better though is a pair of 30/35m halfs - I cut down an old pair and they are ideal for outcrops.
I think the "holy trinity" of ropes, which every all-rounder should own is:
1 x skinny half. Your mate brings the other one.
1 x skinny single. Use it as a single or a half, if your mate hasn't got one.
1 x chunky single. Wall, sport, sea-cliff abseils.
Lengths of these is however a further discussion!