i have taken a couple of them. they are simply majestic. they are notoriously unforgiving to the slightest shot misplacement. i know a couple of hunters that will take them with smaller than a 270w, but i believe the 270 to be the minimum. the local Oryx tends to present longer shots- 250yards and beyond.
it was this elderly gentleman's first Gemsbuck(Oryx) hunt. i "guided" him and he took it at 220yards with my 300H&H.