There are several major cut off points for stats. They seem to be at 25 point
spread:
75
100
125
150
175
200

I have sold items at a vendor using my 90 chr High Elf Cleric, and my 175 chr
High Elf Enchanter (in full charisma gear). The Enchanter get's much better
prices (30-50%) even though the Cleric has better faction.

Also true of agi- check out your AC changes at those cut off points. Normally,
I think it's 1 ac for 5 agi, but from 124 to 125 my AC (on another character)
justs up like 38 or 40 points.