As you can see, the difference between 2048 and 1024 is almost impossible to tell. Then, the difference down to 512x512 is acceptable as well. Only when you get to 256x256 does it make any real important difference.
In the smaller version, the difference is even less noticeable (obviously). For a third person game, for example, you would probably never see the gun any larger on the screen, except perhaps in a cutscene.
I was surprised how sharp it stayed at such low resolutions.