Unless you have godly equipment available, Fire Blast is the way to go.
When synergized by the Lightning traps it will start doing 1000s of points
of damage.
As for gear: you can shop +3 Traps (primary slot) and +3 Shadow (secondary
slot) claws from NM Anya.
Treachery isn't too out of reach, if you're lucky with an NM Hellforge (or
unlucky with a Hell Hellforge, although that's still a bit out of range

). (I'm not sure Treachery is available in SP though)
Lore is a cheap runeword for a hat... Otherwise gamble circlets/coronets.
Regards,
Patrick.