In reply to Tim Sparrow:
My partner and I have stood in the nick at the foot of the Nordkante, looking across the face that the Cassin Route takes.
I gather the climbing's not technically all that frightening, but it's a monster of a face. Just getting on to the route looks like a mission to me. And once you're on it I gather the route wanders all over the place. There's 22 pitches of it, so you won't be abbing off in a hurry.
I suspect it's the kind of place you could very easily zoom up in 9-10 hrs if things went well for you. And die on if they didn't.
It's not one of the six classic faces for nothing.