Re: Actual cold sorc build?
If you want to do PvP, you should stick to only one element and synergize it as much as possible. You might consider extending into Energy Shield, but you'll only want one (strong) attack. Blizzard or Frozen Orb can work here. FO will require better gear to be more effective.
If you're willing to drop PvP from your requirements, you can just pick whichever spell sounds the most fun (20 points) and put 1-20 points into the Cold Mastery and 20 points into (at least) one of the damage synergies (preferably more investment in additional synergies). Then if you want a backup attack from another element, you're mostly stuck with a choice of Nova, Fireball, or Firewall (Meteor can work too... but I'd take Firewall first).
