>After verification, the use of the At() method as is is crawling down when I have to search into a 20k string. If I comment the At() line, it is fast. So, I have an issue I am trying to resolve now. I do have the content into a StringBuilder. So, at first, this is why I created this thread to see if there could be a better use of such implementation if I would go directly into searching into the StringBuilder. But, as is, that method is awfully slow when the string is over 20k. I do not know how to optimize this issue.

Take a look at
http://www.questionhub.com/StackOverflow/1031292

and

http://www.delphipages.com/comp/fast_strings-5279.html