I feel I ought to weigh in in favour of Alistair's 5tet, by the way. I was involved in the recording (I made tea and stuff) so I do know it quite well. It's barking mad of course, but in the best possible way, and really rather wonderful. And leaving aside the question of the soprano in the last movement, the demands aren't really all that onerous. All you need is five of the best string players around and a couple of weeks solid for them to rehearse....
Seriously, I'd travel a long way to hear it again, and there aren't all that many pieces of which I would say that.