Having grown up reading the writings of JOC, along with others such as Jobson, who sang the praises of the 7X57, I eventually had to have one myself. I ended up with a Model 70 Lightweight, and have had it for well over 20 years. By far and away, the biggest percentage of my deer have been killed with cartridges in the 6.5 to 7 mm range. That includes the 6.5 Creedmoor, 6.5X55 Swede, 270 Winchester, 7X57, and the 7-08. I've killed at least twice as many with the 270 than all the others combined, and consider it to be best deer killing cartridge I've ever used.
If one is to believe everyone they read, they might end up believing that certain cartridges are "magical", in their performance. I think that's what we've been led to believe about the 7X57, as well as several others. I've read all the books that Karamojo Bell wrote, and we all have heard the story about all the elephants he killed with the 7X57, and how "magical" it seemed to be. However, Bell also killed a slew of elephants with other cartridges also, and often commented as to how it was the reliability of the excellent German made ammunition that led him to use the 7X57 so much.
The 7X57 is a good cartridge, otherwise it wouldn't still be around after over a 125 years. But, to be honest, it's not any better than any others in it's range. It's still hanging around, mostly I believe, on the account of all the nostalgia connected to it. There's nothing wrong with that either, as I like the idea of using a cartridge with all that history behind. Use it, and be happy with it, as I have done myself.
Apart from nostalgia the cartridge length which lends itself to a standard length action coupled with reasonable recoil are about the only reasons I can think for owning one...or picking one up cheap.
