Couldn't be simpler to Root this handset - install Framaroot from here
and select the Gandalf exploit. Took a couple of goes to take for me and now Rooted!
[UPDATE]Immediately after obtaining Root I was notified of a brand new firmware update for the Padfone Infinity, just wanted to let you know that OTA Rootkeeper from the Play Store will allow you to backup and then restore Root after applying the update. Oh, and the update isn't 4.2, in case you were wondering.