In reply to tnj: I don't think 10cm screws are CE rated, hence the guidance for progression/aid only. Doesn't mean they're useless for protection though.
Take a look at this: strikerescue.com/file_download/1
I think they only tested Grivel and Petzl screws, which I think are 13cm screws but they still reported respectable loads placed facing downwards and in *good ice* - which is the key thing no matter what length the screw