Blood Boil vs Scourge Strike

[skmage]

I was looking over Skullflowers guide and he is saying to Blood Boil with 3+ targets. So should I be Blood Boiling for Iron Maidens? I was under the impression that it was 4+ targets.

[Schizoide]

IF Less than 3 enemies would be hit by Blood Boil,
THEN Scourge Strike/FeS.

ELSE
IF the damage you're doing to those monsters isn't meaningful (In other words, they don't need to die or they heal themselves, so it's just padding)
THEN Scourge Strike/FeS.

ELSE
Blood Boil