Not sure if anyone has gathered any numerical evidence on CHA, but it is pretty easy to have a subjective test by removing CHA gear and trying to charm the same things you've been XPing on. Charm "seems" much more reliable over 200, 225, etc. Especially when charming mobs that are fairly close in level.
At level 45 and forgetting to buff Radiant Visage in Grobb, I was having a miserable time. With the CHA buff, and back up to 231, things went much smoother. This was against the level 39 guards, btw.
Subjective, yes, but it is pretty easy to tell the difference (so it seems). If someone has actual numbers, I am sure they will post.
That said, I wouldn't bother to compare to TLPs since those aren't even the same game anymore.
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