Taos
I am not from "down under" but I have hunted quite a bit with my doubles.
My longest shots on game are as follows:

With my 450 No2 I have taken deer at 85 yards with 350 grain bullets.
I shot a bull elephant at 120 yards with 2 480 grain Woodleigh solids.

With my 450/400 3 1/4" in Alaska I shot one caribou at 85 yards and one running full speed at @125 to 150 yards. [Sometimes you just get lucky

] This rifle has a 50 yard standing leaf, I had flipped up the 100 yard leaf for the shot.

With my 9,3x74R [scoped] I have shot a coyote at 271 yards, lasered after the fact, and hit him with both bbls.
In Africa I shot a Kudu at about 300 to 325 yards. I hit him with 3 out of 4 shots, I did not hold high enough on one of the shots, it hit right under his chest.

I have shot the iron sighted doubles on a rock at 200 yards with the 200 yard leaf flipped up and both rifles were dead on and seemed to regulate well.

Comparing iron sighted doubles to iron sighted bolt rifles and scoped doubles to scoped bolt rifles in similar calibres, in the feild I have not found their to be any great accuracy difference, and I much prefer the 2 quick shots of the double rifle.