The important thing about structuring a speech is to have an evocative opening and conclusion-don't follow the traditional essay structure if you want good marks for speeches-because it is a speech after all, not a spoken essay, although the main body paragraphs is quite similar. It is a challenging task since you have six minutes, you should either decide whether to have four very short paragraphs or just two extensive ones. Some ideas to get you start thinking include in Paul Keating, he is challenging the established idea that what is lost is bad-particularly when you can't regain it-such as military sacrifice, he is using the concept of what is 'lost' as a platform to inspiring individuals to look forward to what can be gained through national unity and appreciating the value of peace. Furthermore, other speeches you can consider include Anwar Sadat-he is challenging the idea that strict diplomacy will give rise to peace, highlighting instead that honesty, integrity and political transparency are the absolute key to a good faith negotiation, and incorporates some very powerful religious allusions to bind his audience together.
Margaret Atwood is another brilliant speech to consider, she is challenging the established idea (even putting aside a feminist interpretation) that there are adequate literary models, but revealing the importance of having more morally complex female characters-not just purely villainess like 'Snow White's mother' or purely good like Snow White herself. This is equitable measure since there are already morally complex characters, the importance of assimilating what is a part of human nature and translating it into literary interpretation can translate to real life equality.
Another speech of note is Noel Pearson-because he is challenging the established ideas about legal fictions such as terra nulls and placing a very firm critique about the incompetence of politicians in their adherence to the 'popular vote' rather than conscience and lacking any moral leadership, to fail repeatedly in enacting some justice for the Indigenous people, where the case about the failure of the Aboriginal Protector to protect Aborigines epitomises a lot of these things. This is very thought provoking as not many people would have the guts to openly criticised John Howard to such an extensive extent-using some political satire to make it subtle as well.
Hope this helps
At the end of the day, the most important thing to remember is that YOU MUST ANSWER THE QUESTION AND NOTHING BUT THE QUESTION TO GET THE BEST MARKS