haniel
If your willing to take the risk for doing the extension for History, it's basically more research and writing, like normal history (ancient/modern). The scaling should be great if you do well in it I guess, many people struggle at first but it gets easier by time. The teacher in charge is important as well, if the teacher is willing to take their time for the class or for you individually, then it will be good then to choose History Extension. Hope this reply isn't to late, best of luck for the future.
