In reply to /tmp:
When I did it, the Bosse was merely a slight steepening we walked up, and we romped along the ridge until just before the summit block where we were slowed by a nasty, v exposed pitch of 50 degree hard, black ice that required an ice screw belay, and two axes (it would have been doable, but tenuous with one).
I'm really usure how genuinely informative comparison with Scottish winter grades are – the factors covered by the grades can be very different. And how does one meaningfully factor in the seriousness of a descent (eg on the FA) in a comparison?