In reply to Dim Dringo:
I've done the Sth Ridge but not the West (which looks incredible!) and one thing that I'd be bearing in mind on the basis of that experience is that it's a short descent off the summit to a snow-field and running water a bit below that. In the dark, it might well be another matter: the route is marked but it's not always obvious. Overall, it's a pretty short descent from the summit to the hut.
However, if you were to be benighted on the summit, there are good bivi spots and obviously you'd be pleased you'd carried the extra weight up the S ridge.
The staff at the hut are amongst the friendliest and most helpful I've encountered.