I would tend to agree with NitroX and that is based on using the 300 Hornady round nose in 375 and the 500 grain Hornady in 460 Wby.

The times when I have mostly seen these calibres do the big damage is with gut shots. They often seem to empty the whole gut on the ground.

If I had to make a guess I think one of the reasons that the Australian Big Bore shooter will have a different opinion to the American is because of the volume of "white tail deer" size animals that are shot and also because a lot of the animals will get hit in the guts. In addition we are not looking at "meat damage"

In my experience if you went out and shot 100 kanagaroos with each of the following calibres:

243
270
308
300 Magnum
375
460

and then from each 100 animals shot you selected the 20 animals with most external damage then the 460 would easily be the winner and the 375 H&H next.

One of the things that I have found is that harder bullets often produce the most external damage. For example the big damage I have seen from the 375 H&H has been with 300 grain Hornady round noses, not 220 grain Hornady Flat noses. The 460 had done the most damage with 500 Hornadys rather than 400 grain Speer Flat Noses.

But the softer bullets provide more "instant death". Large male Red kangaroos hit at the bottom of the chest with 300 Hornady Round Nose or 500 Hornady in the 460 often have a huge exit but the animal is alive when you go up to it. But the same hit from a 220 grain flat nose Hornady in the 375 or a 400 grain Speer loaded in 458 or loaded back in 460...and the animal is dead before it hits the ground. Ditto for 308 130 grain Speer Hollow Point.

Mike