What's best size pack for Ice Climbing

Yes, it's light. Lacking some features as you might expect.

Fidgety/fragile shock cord to attach your tools and crampons. 

No side straps for e.g. poles, pickets, skis.

No frame, if that matters to you.

It's smaller than most "45L" packs.

A lot of people enjoy the Alpha and it might work well for you if you like the compromises Arc has chosen, but it's not like they stuffed the same features as other packs into this thing and magically made it lighter.

I'd rather have one of those Cold Cold World packs Allen linked above. Not as sexy as the Arc stuff but to me more functional. 

Went with a deuter speed lite 24 for climbing.  I liked the lifetime warranty and size.  Hopefully it will fit me nicely.