CHA isn't something much brought up here, so I thought i'd talk about it some. First of all, we know about science talking.
The first bit is on zolku (shopkeep)
I believe there's actually charisma talking, up to a point. I made a file for the sole purpose of, and at about turn 530 (note: I spent around 30 moving, so it took around 500 talks) I got a "You feel very confident in your social skills" and received a +1 to my charisma. The second charisma came at about turn 1200. 3rd at late 1800's. 4th at early 2800's. 5th at about 4000th turn. I got a 6th around my 6000th turn.
I replicated similar (though slightly later) results with the priestess of silva. I then moved back to zolku, and talked to him. I got the 3rd around 2300.
Edit note: This change of 2300 turns on Zolku reflects the original check, being of a -1000- turn difference from CHR 13 > 14.
It's possible that it's caused by switching targets, or it could be due to the fact that I started this file with 11 CHR base, instead of 10, though it seemed not to affect the priestess.
I'll be dicking around some more in new attnam to look at it. I'll likely use wizard mode at some point, and a belt of levitation to test it in Attnam also. It's be good to see if we can assemble something like a "Charisma Talking" chart, in order to benefit charisma.
It's a pretty negligable bonus, but it's all about the journey, right?
Edit 2: I re-talked to the priestess with a base of 9. Got +1 at the 250ish mark. I repeated this on the same file (using wiz mode to drop my CHR by 1 everytime it went up) and the bonus consistently landed around 250-300 turns. Zolku took consistently longer, around 350-450. This seems to indeed suggest that certain character are much more beneficial for "Charisma talking" than others.