As a PH, I offer clients, who do not bring their own rifles, a choice of 4 calibers, a 6.5 Creedmoor, a .30-06, a 9.3x62 and a .375 H&H for plains game hunting. The 6.5 CM and the .30-06 are the most popular. Both are supressed, which probably has something to do with it. If a client shoots the .30-06 as well as he does the 6.5, I recommend the .30-06, otherwise the 6.5 CM.
6.5mm rifles have been killing plainsgame in Africa for more than a century, the 6.5x54, 6.5x55 and 6.5x57 all used to be popular. The 6.5CM can do what those calibers did without any problems. Added to that bullet construction have greatly improved.
My two personal 6.5CM's have accounted for 959 head of game, including 30 black wildebeest, 66 blue wildebeest, 57 eland, 31 gemsbok, 29 red hartebeest, 3 sable, 25 waterbuck and 8 zebra.
If it did not kill cleanly and reliably, I would have stopped using it long ago, nobody benefits from tracking wounded game, least of all a PH.
Before I started using the 6.5CM, I used a 6.5x55 as my light rifle, that rifle, in my own hands and those of clients accounted for more than 1200 head of game, before the barrel gave up the ghost and I had it re-barreled to 9.3x62.
I do enjoy using different calibers and regularly use, apart from the 6.5CM, a 6mm CM, 7x57, .30-06, 9.3x62, .375 H&H and .416 rem mag. Arguing about calibers is great fun, but honestly if most hunters spent less time worrying about calibers and spent more time actually practising their shooting skills there would be a lot fewer wounded animals.