A Ber for 20% CB isn't too bad an option either IMO.so either a 40/15 ED/max, an Ohm (don't know which would boost dmg the most) or a Lo rune for some sexy 20% Deadly strike (20% to do double damage!), do some calculations to find out which is the best.
True! Depends of the use of the Axe though. Without CB in the weapon he needs Gulli/Gores/Rattlecage or Duress/Steelrend (Crafted CB gloves) or combinations to reach a satisfying level. For ubers I would say that a minimum of 50 CB is preferable. With CB in the weapon more choices of equipment is available.Crushing blow is quite weak against most monsters due to their low HP, so when killing things that are sped up with crushing blow you could get it from other gear, while being able to have a higher-damage-no-cb weapon for the rest of your gameplay.
Why would you want to take down hell baal in 8 players? If you want drops, do it solo, and if you want exp you go in an 8 player game anyway where people will leech the drops (and will cast static field anyway). Not to mention you actually have to find a game with 7 players in it where none are going to baal. If it's single player, do /players 1 before baal. If for some reason you choose to solo level *and* actually go and kill baal I suppose CB can help there too. But that's still a rather small portion of the game when you also consider 8 player baal runs for exp, lvl85 areas/pindle runs for MF...
And again, CB gear can be swapped, the socket cannot.