I think its more important who your going to get to tune your car.
As adrian said choosing an s300 gives you more choice with tuners.
Like myself I have a s200 no one in brisbane tunes s200. There are a few who tune s300 in Brisbane so choose your tuner and see what he can work with.
Your lucky your from sydney cause there are many reputable tuners down there. Personally I wouldn't have any locals from brissy tune my car.