Just get the 1000, then no worries if you have enough power or headroom. The Dually is a great cab, but I'd go for something local that you can try first. Shipping a cab from the US to Australia would be crazy expensive. See what's in ready supply on the used market, then you can find a good deal. A good sealed 810 would get the job done. Dunno about there, but here there's always a few used Ampegs selling locally for good prices.

