I took my gemsbok and blue wildebeest last year with a 300 PRC and 208 Barnes LRX at 2850. The gemsbok didn’t go far and it went down after two shots - first shot through the lungs (though not the shoulders) and a quartering away shot as it was running in a half circle. Took two more shots to finish it though when we approached it - they are tough!
I took another 7 animals - baboon, eland, impala, kudu, jackal, blesbok, and springbok. As you might expect, the jackal, baboon, impala, and blesbok were DRT. Unexpectedly, the wildebeest was as well on a frontal shot at about 125 yds that went through the heart and ended up in the pelvis. I hit the springbok a second time on the run before it went down, though upon examination it was clear the first shot was deadly. The eland and gemsbok took 3 and 4 shots respectively despite initial shots being through the lungs. My PH did instruct me to keep firing on the gemsbok and the eland as long as they were in their feet.
A couple of conclusions I drew: for anything larger than an impala in Africa a 30 cal magnum is not anything close to too much gun, monometals provide reliable penetration but not the fastest kills, put it on the shoulder (I knew this but did not always do it despite studying the Perfect Shot 2), and gemsbok are as tough as advertised. My impression is that eland aren’t that tough, but they are HUGE so you might as well consider them the same.
My light rifle is a 6.5 PRC though it hasn’t been to Africa with me. From what I’ve seen, the 6.5 PRC (and CM for that matter) are a sensible MINIMUM for Africa, but hardly ideal for any of the plains game. Also, bonded bullets and monometals are a double edged sword guaranteeing penetration and ADEQUATE expansion and are deadly, but do not result in catastrophic tissue damage and fast kills.
Know your bullet and it’s performance window. Using a deep penetrating bullet in a marginal caliber for the game size and toughness you’re targeting will result in reliable, but slow(er) kills. I’m not surprised at all by your friends experience with the 6.5 PRC. A bigger cartridge with a lead bullet will kill faster (as long as you can shoot it well and it can be expected to penetrate through the vitals.