The difference between 200 charisma and 75 is close to one mob level of resistance.
Mob level is the most important factor for charm breaks. Then mob magic resistance. Lastly, player charisma.
The best way to charm is with a partner that can grab agro and die first.
[You must be logged in to view images. Log in or Register.] Movement speed is your best stat for charm soloing. AC has a fairly steady 2 to 1 value over HP.