Thanks for doing that research. I never shot either of those animals, but during my African phase I did a whole lot of reading and listening. The hyena is not tough like a buffalo but is still pretty big and ornery. A 7 x 57 would would smoke one for sure, but I would still feel better with a bit more power - 30-06 or better. The one I saw shot was with 375, so enough said. The thing about a croc is, it has to be hit just right or you will lose the animal, and the critter's brain is not very big. If you can drive tacks with a 243, great, but just remember that if you are sighted for 150 yards and the range is 40, you will hit low. Most people usually only take 2 rifles to Africa, so whatever you use for plains game - 308, 30-06, 7 Mag, what ever, that's it. Just get real good with it.
By the way, I have shot warthog, and I would never consider a varmint-type load. The vitals are protected by so much gristle that a true high-power rifle is essential. 270 is great, my 300 Mag seemed about right. Mine pegged the scale at 300 lbs, and after cutting it up and looking at it, I wished I had my 338.