It might be easy to group the PhB and R&D into the '99+ ATAR points club' now, but remember that they are in fact different degrees, even though they both have a heavy research focus. In the first year they can be very similar, but in second year the engineering degree starts to branch off into less theoretical physics and maths, and more practical applications and problem-solving. That does not, however, mean it becomes any easier.
If you like practical problem solving using science, as well as more 'theoretical' science, you could always do a combined degree B Engineering (R&D) / B Science, which is what I'm doing, and from what I have been told is in fact what most R&D students do. The theoretical knowledge of physics, chemistry or biology (for example) complements the research and development focus of the engineering degree. (Also: In your electives don't feel pressured in choosing maths-focused courses, it's absolutely ok to try something different, like philosophy, anthropology, environmental science or politics - and electives can be a good break from your main courses.)
I applied to the R&D program with a high 98 ATAR, and had no problems getting in. When I went to one of the advisory days, they said they might want to look at my maths score to make sure I could 'cope with the course', and after that it all went smoothly. One of my friends applied with a lower 98 ATAR, and he got in as well. The fact that he did well in the ANU secondary college physics program helped his cause. Other friends in the program got 99.2-99.95 ATARs and of course also had no problems applying and getting in.
As for the PhB, I have several friends in that program. If you get above 99 you have a good chance of getting into the PhB. If you don't get in, the B Science (Advanced) program is good too. It's not all about your marks, give the PhB a try first. They generally like to meet with you when you apply and talk to you about your motivations to apply to such an 'exclusive' degree. Don't worry too much about the extra-curriculars, they don't play such a big deal as long as they can see you can engage with other people and have a multitude of interests outside of academic study at school - in other words, that you're also interested in and capable of learning on your own.
In fact, that's a big theme at university: managing your own learning. No more hand holding, it's up to you to manage how you pace your learning; whether you go to lectures or watch them online; if you buy the recommended textbook or find extra sources for learning; or if you spend an evening studying or at the ANU bar. Nevertheless, you'll meet lots of interesting people at the ANU just like you - especially in the PhB and R&D degree. Both degrees have their own little communities that have guest lectures and lunches every once in a while, and are very supportive of new students.
You can expect ~20 contact hours (ie. a mix of lectures/tutorials/labs/pracs) per week, with a total recommended workload of 40 hours (or 10 hours per course). What I have found though is that is a conservative estimate, you'll find yourself spending a lot of time doing the assignments, especially in MATH1115, and simply keeping up with all the courses. Also worth noting, it is expected of you to get a HD (80%) average to stay in the degree, otherwise they will shift you into the standard engineering or science degrees. But don't worry about that now, if you're generally motivated and have good study habits you'll do well in the PhB or R&D, and most importantly you'll enjoy your time at uni.
