$Configuration['Vanilla']['Comment']['MaxLength'] = '2000';
Lincoln, I just added that line to the config file and am still getting the character limit for the body post. http://screencast.com/t/EzOm9QSXr.
perhaps you didn't set config statement correctly in config.php
if you just added the above statement you reduced it to 2000.
try changing comment length in dashboard in your forum -> floodcontrol
if there is no line in $Configuration['Vanilla']['Comment']['MaxLength']
8000 is the default number of characters.
16000 is 16000 characters. = put the number of characters you want.
$Configuration['Vanilla']['Comment']['MaxLength'] = '16000';
I may not provide the completed solution you might desire, but I do try to provide honest suggestions to help you solve your issue.