I think Mafia runs pretty much on anything.
Your processor is strong enough to run it. The problem is the game being an old game, it only uses one cpu core for everything. Given that be aware of the draw distance setting on the widescreen patch configuration ini... Even more "recent" cpus like yours can have a difficult time rendering the whole map.
Given that you're using windows 7 I would use dxvk (google the last version still compatible with windows 7) with your gt 710, as your 6850 doesn't support vulkan.
If you're willing to give 6850 a try first, try to disable Hardware T&L (or enable Software T&L, I don't remember how it's called) and see if that makes a difference.
Cheers