i tried this and it helps me, my upgraded install from 2.6.x to 2.7 is now fast as the old installation. here are my modifikations.
Try disabling all external HTTP access:
1. /wp-includes/http.php
2. this on about line 210:
function request( $url, $args = array() ) {
global $wp_version;
3. Change it to:
function request( $url, $args = array() ) {
return;
global $wp_version;
4. Save the file and upload to your host, Open the admin again and see how things fair, Report back on if its helped or not.
http://www.gpunkt.at
