If I still lived in Western Kansas, it would probably be the 6.5. However I live in the Florida Panhandle. Heavily wooded.
For me just about any high powered rifle would do.
For a SHTF scenario, how many engagements are going to be at 1000 yrds? Unless I shoot out over the ocean here, I don't see the application. I do think for actions within 50 yards, a 12 gauge will be just fine, or an AK or an AR 556. Inside the wire, "say hello to my little friend", no further comment.