OK, just want to let you know that I decided that we will implement a speech skill on top of the charisma attribute.

The most important reason for this decision is that it seems like you really want it this way. If you tell me you would have more fun with the game if you have a speech skill in it, this is the strongest argument.
Second reason is that it's easier to raise your ability in talking to people with a skill as with an attribute.

So, thanks to everybody who pushed me to change the rules that way. You were right. I'm convinced of this idea.