Quickest way to send data to javascript?

I’m creating a php website which uses javascript (jquery) to draw a google map and place up to about 500 markers.

Currently, php creates an xml file for javascript to read and place markers accordingly (loosely based on this tutorial -http://www.sitepoint.com/google-maps-api-jquery/)

I have < 2meg connection, but it is quick enough on latest browsers. IE 8 is REALLY slow to both draw initial map and sometimes gives up before placing markers.

Tried ditching the xml idea and using httpRequest instead, to get the info real-time from php. It works, but the markers appear really slowly.

Just wondering if there is a quicker way to pass the information to javascript?

Each marker needs id, longitude, latitude and title.

php currently uses a session to store an array of place ids (the result of a search) and then looks up other info in mysql.

Would appreciate any advice on the best way of getting my marker info into javascript.

How about having a php file that responds with javascript code, and having the HTML page request the javascript code from that location?