Considering you like the 223 for deer and you desire a big gun, I would consider the next step up, a 243 as your big gun.
Therefore I vote the 243. Of course you will need an 1/8 twist.
You can use the various 105gr slugs and slay deer at long range, with better ballistics than a .223 bullet.
And by chance if an elk accidentally crosses your path while deer hunting you can put the hurt on him with confidence!
