I started with the .308 then added .223. I considered the .223 more of a "plinking" round that I could afford to shoot more of, and enjoy the reduced weight and recoil. I then "accidentally" got into .243 Win. when I purchased a Mauser I planned to rebarrel to .308. After firing it first I had another caliber added to the stable. I was impressed with the ballistics, accuracy, and mild recoil from a .308 size case. Which brings me to my latest "new" cartridge, the 6x45. It is simply a .223 case necked up for a .243 (6mm) projectile. Since I already reload the other cartridges, it fit right in with the purchase of a barreled upper, and a set of dies. Nothing else required. I plan to build a 6x45 bolt action Savage. I haven't eliminated or replaced any of the calibers, merely added more choices with overlapping use.Why the need to "replace?" Just add something to fill a perceived role. If .223 is too weak I'd go straight to .308.
Give the 6x45 a look and test drive one if you get the chance.