I personally find advanced harder than both extension 1 and extension 2 english because of the amount of texts you learn through out the year and the competitive nature of the course. At my school, they didn't even offer standard english as it's apparently a huge trap for your atar. However you should definitely run your concerns by your teacher as they should know the extent of your ability.
HSC 2012 - advanced english, extension 1, extension 2, 2 unit mathematics, biology, visual art
HSC 2012 - advanced english, extension 1, extension 2, 2 unit mathematics, biology, visual art