if 80% of what you shoot are small deer like Roe, and also some vermin, with the odd sika or red deer stag thrown in, the .243 is a stunning in performance if loaded right and shot positions are appropriate. I'm off this weekend to cull maybe 3-5 red deer hinds, rifle coming out of the cabinet,.. .243Win. Why are the big guns staying home? because there's no need, the hinds, calves and yearlings usually drop just as fast, in fact, much faster than if shot with a 30-06 and a 180g nosler partition (experience this plenty), AND, the game dealer is MUCH happier.
I can see however, if you were only allowed 'ONE GUN', and you might want to go for boar or plains game, etc in your life, then that 'one' would probably not be the .243, but a .308 (or 30-06 or 7x57 for that matter).