Why in particular do you need such high ability scores?

Throwing most everything else down the drain, you can get a 17 in wis and 20 in charisma(post +2 racial mod to CHA) on a 25 pt by, but you will have to be high enough level to afford to make or buy a charisma headband, or at level 4 increase your charisma by 1 to 21.