Ajax via JSON or Delimeted String

Ajax via JSON or Delimeted String

I have a project I am working on that is currently receiving data via ajax in the form of plain text that is separated by \n, |, and :.    Once I receive the data, I have to split it accordingly with javascript and then update dom elements using the .html() method.    My question is, what I gain performance if I returned json data instead of a delimited string?   My web application performance great in modern browsers, but in IE8 and below, it gets very slow with large DOM updates. What is the best method to constantly replace html content via an ajax data set?