Weapon is personal preference. If you want to use a shield, go with a Valhalla+Acumen. If you want a mage blunt, go with a Staff of Evil Spirit.
I used a +3 (+5? I forget) SOES for B-grade and it was great, made all skills land constantly and had good MAtk. The only drawback was going without that additional Acumen boost; even with +4WIT and an Acumen pot, it still felt S-L-O-W after using a Homunkulus+Acumen.
Also, think about the role you will play. If you solo or duo, you need to cast quick and kill the mob before it gets to you (especially if you use Curse Death Link, ugh). If you party all the time (and I mean 5+ people), you should really be using your debuffs and curses - so MAtk becomes more important than cast speed.
I agree with L2Girl, Avadon is a great armor. Again depending on your role, you could try Zubei Robes for the additional MAtk - just remove the gloves to regen MP.
I think that a SOES + Magic Focus will do just fine because you have the summon with transfer pain and you really need very big dmg in pvp fights.
For Robes i'll choose Avadon.
:)