Sorcerer tips for later bosses

Any tips for Seath? Think I'm SL55 with homing soulmass, crystal soulmass, crystal soul spear, and magic shield. Don't seem to do much damage with spells or my magic longsword+5.

4Kings are currently kicking my arse but I should have them in a few goes. I tried BoC and I thought fuck it I'll deal with you later.