I'm after a alpine pack in the 30-40L range. I have been looking at the black diamond page and as a newbie, kind of bewildered by the range available. 
  
has anyone had experience with the black diamond speed, axiom or axis packs, or can recommend any other packs in this 30-40L range? any particular features to look for other than crampons + ice tool attachments? 
  
and do people find 30L enough for those 1 day alpine assaults with emergency bivy gear or is 40L more recommended? 
  
All comments greatly appreciated!