In reply to JeroenandTimo:
I have a 50, and some very long slings. Sometimes I used it in Costa Blanca, sometimes I have used a 60, which has been fine for almost everything.
We bought a 70m 3 years back as advised in the guidebook. Used it once, handy for multi-pitch, and then once more when I went off-route on a bit of an epic and was v grateful for the extra rope! Otherwise, it has sat unused, far too much of a hassle to flake out and carry about. But I don't like a hassle!