Well, I'm fairly sure you're safe, Zapmeister, Zen's wrath was probably directed at me.
Well Yossar, I suppose you'd be right. It's only bad if you casted with the bare minimum of skill. But how much skill do you need for it to match the economy of the level 3 spell?
I'm using these numbers, which are from memory:
1 frost fiend/6 slaves for the basic spell.
base of 6 frost fiends/50 slaves for force spell.
Every level above min gives 1 extra fiend
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Each fiend costs (slaves/fiends) 8.33 slaves using force at 5 blood skill.
Each fiend costs 7.14 slaves using force at 6 skill.
Each fiend costs 6.25 slaves using force at 7 skill
Each fiend costs 5.55 slaves using force at 8
You start getting more economical at 8 skill, make of it what you will...