Personally, I don't see the point in having similar calibers, much less two guns in the same caliber. I understand everyone's point and I see the logic in it but I don't tend to go that route. (I do however, have multiple shotguns in the same gauge but all the duplicates are hand-me-downs and they have become the backup/loaners)
My primary deer rifle is a 7mm-08 Rem. 700 Mtn rifle. My loaner/backup is a 700ADL in 30-06. If I ever get to hunt Elk, I'm all set. I also have a Knight Disc rifle and T/C White Mtn. carbine in .50 cal. that serve as primary and backup muzzle loaders. They, of course, could serve as loaner/backup during the regular season if I needed them to.