About the previous note from Davey:
ob_start(array('ob_gzhandler',9));
Does not work. The output size isn?t affected at all, stays the same.
ob_gzhandler compression level use zlib.output_compression_level, which is -1 per default, level 6.
To change the compression level on the fly, simply use ini_set:
<?php
ini_set('zlib.output_compression_level', 1);
ob_start('ob_gzhandler');
echo 'This is compressed at level 1';
?>