I always went heavier than that. I use an olde Manfrotto/Bogen 3050 (or maybe it is a 3051). Bigger is better -- the Cambo monorails with long rails are heavy and unweildy. I find a big and heavy tripod tames the camera better, especially when used indoors in a studio to take portraits as the OP intends... or near the car trunk when taken into the field.
I've used Tiltalls indoors and outdoors with cameras up to 5x7. A heavier tripod would be better when the wind is blowing, especially with long exposures.
The OP is looking for a tripod to use in his studio so carrying it around is not an issue. He just wants something to support his camera and won't break the bank.
Why buy a Tiltall that may just get you by when you can pick up a rock solid Majestic for just a little more money?
On occasion I have also seen studio stands go cheap on Craigslist. Yes, they are more expensive than a Majestic but they are really nice if you have the room to use them.
Seeing as all this has to be shipped all the way to Australia, perhaps a Bogen would be a better choice for tripod. Within a studio setting I suspect there is not much wind. My 3060 with P3 Gitzo head would be much cheaper to ship and it handles a Deardorff V8 in any wind.