Ley
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I did the same thing: 7 -> 11 -> 16. The spell bonuses simply add up. Maybe you had a regular speed boost (which adds +3), and not an expert/advanced one.
I don't think speed bonuses can stack... Maybe it's like this: regular +3, advanced +4, expert +5? (I mean specifically in this example).
"Единственное, что можно сказать с уверенностью об удаче - она изменит..."