Well of course a 338 or 375, shot well, will kill plains game. The class of cartridges consisting of the 7-57, 270, 280, 308, and 30-06 will do just as well with good shot placement and a good bullet.
I just returned from 22 days in Namibia. I shot 52 critters ranging in size from springbok to wildebeest, all with one shot from my 270. I used TTSX and bonded core bullets. This was trip 18+. I have used the 270 and 280 mostly. Shoot well and you will find the critter about 25-30 paces away. Easy peesy!
My PH's both used 7-57 and 308 for their hunting.
