In reply to jaamez:
I've used a 30m rope in Summer which was absolutely fine.
However, I assume given the time of year you are thinking about Winter conditions. If it was me I'd probably take the 35m single over a 60m half but I wouldn't be too concerned either way.
However, I've done the ridge at least half a dozen times in Winter. If you haven't done it before, a longer rope does give you more flexibility.
Post edited at 00:28