In reply to CurlyStevo:
Cascade has seen quite a few fliers in recent years, to the best of my knowledge none of them have ripped the belay but there is definitely some scope for this. So yes, serious but I remember a similar scenario almost playing itself out years ago on Comb with crap axes and inadequate movement skills.
If you take Cascade direct (instead of creeping along the ramp) it is definately grade V ice-climbing, comparable to the main pitch on Hadrian's. It gets IV,5 because it's short, but is a fall from the main pitch any less serious than one off Hadrian's or the Point? Depends whether you go down to the Coire floor I suppose..
You know what to expect from it and so did I, so I didn't do it until I had grade V mileage and it still felt sustained and a little scary. But other people are clearly looking at the IV grade and not the tech 5 and consequently getting into trouble.
V,4 wouldn't seem right somehow; it would make it the same grade as Zero Gully which is (anecdotally) a protectionless horror-show with poor belays.
I think the crux of the issue may be that the split grade system is applied differently for mixed routes than to ice. On mixed it appears to be much closer to the rock equivalent, where the tech grade is for the crux move. On iced it appears closer to European grading where the latter number describes the overall physicality of the pitch (on easier ice there is often no discernable crux).
Easy to work with as long as you know that there is really no correlation between a cruise of IV,4 ice and consequent struggle on a mixed III,4.