For deer, varminting, maybe elk and maybe a sheep or goat some day.. for an extra barrel on a single shot lightweight rifle.

which would you choose and why?

reloading myself, so ammo is not a problem.

It would seem to me that it will be about as difficult (or easy) to find brass for either. So get the biggest one.

Jameister the 7X65R is the more popular of the two. At one time I had owned a 9.3X74R in a number one. It was a very ordinary rifle but shot well. The way things are going for my 500 N.E. 3" project, I might just build another 9.3X74R though I would do things diff. I always wanted a 7X65R (since I like the 280) in one of those sweet Dakota arms singles.
we live in the metro area ... maybe if I am free sometime we can shoot
take care
smallfry

If you're determined to have a rimmed cartridge, I'd go with the 7X65R. Especially given the variety of game you've mentioned. As was noted, it's basically a rimmed 280. Living in the States, either one is most likely a handloading proposition and the 7X65 will be more flexible.

What an elegant cartridge. I'd love to have a 7X65 some day.

Can't you form 7x57R from .444 Marlin?

Gentlemen

The most popular is 7X65R in Europe soo why bother with a slower and less common round like the 7X57R.

This would be my no1 choice in a single shooter for deer size game