I've used both the 7x57 and .30-06 in Africa considerably, and the only real trend I've noticed is that both is that really hard, deep-penetrating bullets kill quickest, on average, when muzzle velocity approaches 3000 fps, as with the 165-grain TSX load JJHack uses.
Have not been impressed with the 160 TSX or North Fork in the 7x57. They kill but sometimes not very quickly. Wider-expanding or partially fragmenting bullets, like the 156 Norma Oryx, 160 Nosler Partition/AccuBond, or even the 160 Sierra GameKing kill quicker on average at 7x57 velocities. (Yeah, I've shot some African animals with 160 GameKings, though none weighing much more than 200 pounds. There were zero bullet failures, and all the animals died quickly.) If I ever take a 7x57 to Africa again, and decide to use a TSX or other petal-type, deep-penetrating bullet it would probably be a 140-grain pushed as fast as safely possible.
Also tend to agree with JJHack's conclusions about the blood-trail difference in 7mm and .30 caliber bullets, but did follow the blood trail of a kudu shot too far back with a 160 TSX from a 7x57 for over half a mile before it petered out. Or at least the indications were the kudu was shot too far back. The bad hit was due to a scope that went screwy--literally screwy, the objective bell usncrewing itself, something discovered only toward the end of the blood-trailing. But we never found the kudu, so don't know exactly where the bullet landed.
Once took a long time to find an impala shot with the 7x57, despite using a wide-expanding bullet that landed in the right place, and exited. The impala headed downhill in very steep, brushy country, and was found around 100 yards away after more than an hour by a Jack Russell terrier. None of the humans, including several native trackers, found a speck of blood except right around the fallen impala. The shot was at a steep uphill angle, so the exit was high on the chest, and the low entrance hole didn't leak--but the impala probably wouldn't have gone nearly as far before falling if the country hadn't been so steep.
That was just one of those things, as the vast majority of African animals shot well with the 7x57 (or the 7mm-08) haven't gone far enough to really need tracking, and 3/4 fell within 50 yards. The animals included many of the supposedly super-tough "plains" game such as zebra, gemsbok and wildebeest. In fact one of the quicker one-shot kills on blue wildebeest I've seen was with a 140-grain AccuBond from a 7mm-08. The hunter put the bullet right behind the shoulder, about 1/4 of the way up the chest, and the bull ran 35-40 yards and keeled over dead.
Of course, bigger bullets tend to kill quicker, but that particular hunter also brought a .300 Winchester Magnum and found he didn't shoot so well with it after three days of magnum recoil. He switched to the 7mm-08 and did much better, because the bullets went in the right place.
Another guy on the same safari (a month-long cull in South Africa) had the same thing happen with the 9.3x62 he brought for bigger plains game, so switched to the 7x57 he'd also brought and killed gemsbok, zebra and kudu with it, no problem. Would have to look up in my hunting notes to see what bullet he used, but no bullet kills well when it doesn't end up in the right place.
