I have a Rigby Highland Stalker in .275 Rigby and used it (exclusively) on my most recent trip to South Africa in April of this year. Those who have read the (long, long) hunt report will know that I took 85 animals with it on that trip. The smallest was springbuck and the largest were two eland, both shot within a minute of each other. One was dead after the first shot, while the other took two. The problem with the latter eland was not the fault of the cartridge, but poor shooting on my part. When I took a moment to calm down and shoot properly, the second shot dropped it in its tracks.
While I wouldn't use a .275 on dangerous game, and I continue to think it's not the best caliber for the larger, tougher antelope, you can certainly use it with confidence on the those antelope (and zebra) if you can reliably place your bullets where you want them.
And best of all, recoil is virtually non-existent, and the rifle is light enough to carry for long stretches without tiring you out. My next-largest calibre is .300 Win Mag, and while I love it too, I can't even imagine what it would have been like to take 85 animals in two weeks with that rifle.