I wouldn't want two of that gun
Seriously though, there's two schools of thought.
The first would be that you get exactly the same gun set up exactly the same way so that you can have the exact same feel if you need to switch.
The other would be to get something completely different, in a different caliber, so that you can have another tool in the toolbox that also happens to be a backup to the primary. Something like an AK would be good in this case, as it's less expensive, shoots a bigger bullet, less prone to fouling and malfunctions, etc.
This is my take on something in between the two. If I was starting from scratch today, I would probably make the brown gun a 6.8 or 6.5 just to have a slightly more powerful option.
While serving two different roles, the two guns in the above link share the grip, vert grip, basic optic configuration, stock, and sling such that they feel almost identical when changing between them, with the magnification of the two optics being the only real change.
Hope this helps