Well, Canberra is a jewel (got that box for Christmas) and leaves your framerates intact (like YMML v2 or better, as it's smaller) while Brisbane seems to follow up on the earlier Melbourne releases in some ways. Not as bad though (fps-wise) but from all Orbx airports I own it's the most demanding. I'm using the 1.10 update there, my initial box release was 1.00 and performed the same.
So a high-clocked quadcore is recommended with the complex and texture loaded birds like the 707. You will surely notice some fps impact at YBBN.
There are some options in the Control Panel to tune then. I currently have them all enabled but it performs on the edge of being fluent on my 4.0 i7 in my eyes. Talking about full UTX traffic, VoxATC and so enabled and birds like 707 or 747-8i.