Except for the red deer, I'd be on board with the .243; I think you guys used to have a slightly smaller cartridge called the .243 Myra (6X43) but you don't hear much about it over here any more. A 200 pound kangaroo, would be exceptional, and since they carry much of their bulk near their back end, the chest density is proportional to a smaller animal, making a high velocity small bore a suitable choice. Red deer on the other hand are twice as big as a Canadian whitetail, and just a bit smaller than an elk. I wouldn't choose a .243 for an elk, although some do; but then some people went after Bengal Tigers with .22 Hi-Powers. I prefer to balance my rifle against the largest game I hunted, rather than the lightest, so I think a .270 is a better choice given the parameters you've laid out, provided the ammo is available. Unless culling great numbers at a single sitting, he'd probably find a sporter just as accurate, lighter, better balanced, and quicker to get on target than a heavy barrel, but its more personal preference than something that's written in stone.
