Fallout 4 : Persuasion Success

What is the maximum Charisma I require to succeed all persuasion (hardest) attempts?

You need 11 Charisma for 100% chance to succeed hardest attempts. This will require clothing or consumables that will boost your charisma past 10.

The only way to have permanent 11 Charisma is to first have 10 Charisma and then collect the Charisma bobblehead.

@vagrantsnow: thanks a lot that was very helpful