The Paradox of the Stone

I am sick to death of people defining God's omnipotence by the capacity to do all that is logically possible. That is not a logically self-consistent idea. We can prove it right now.

1. God is omnipotent (definition).
2. Omnipotence is the capacity to perform any logically possible task (definition).
3. Therefore, God has the capacity to perform any logically possible task (from 1, 2). 
4. If I can imagine some logically possible world wherein some task is being performed, then that task is logically possible to perform (definition of a logically possible action/task).
5. Given any finite rock, I can imagine a logically possible world wherein it is being lifted (definition of possible worlds---the proposition is self-consistent so it is necessarily possible to imagine).
6. Therefore, it is logically possible to lift any finite rock (from 4,5). 
7. Therefore, God can lift any finite rock (from 3,6).
8. I can create a finite rock such that its own creator cannot lift it (observation---I can only lift so much weight).
9. If I can create a finite rock such that its own creator cannot lift it, then it is logically possible to create a finite rock such that its own creator cannot lift it (modal axiom B---actual implies necessarily possible). 
10. Therefore, God can create a finite rock such that its own creator cannot lift it (from 3,9).
11. If a rock is created by God, then God is the creator of that rock (definition of "creator"). 
12. If God can create a finite rock such that its own creator cannot lift it, then God can create a finite rock such that God cannot lift it (from 11).
13. If God can create a finite rock such that God cannot lift it, then there exists a finite rock such that God cannot lift it (definition of create---to bring into existence; the rock does not have to be actual, either; I can simply imagine an element of that set, and the set is officially nonempty).
14. If there exists a finite rock such that God cannot lift it, then God cannot lift any finite rock (from set theory---there exists an element of the set of finite rocks that is outside of the set of things that God can lift). 
15. Contradiction with 6: (God can lift any finite rock) and (God cannot lift any finite rock).  

The logic has spoken, guys. Just give it up already and find another definition for omnipotence. I defy anyone to explain which premise they disagree with.