If you hunt then a 6.8 upper would be a good thing to get. The round is good out to 300 yards for hunting. If youdo go with a 6.8 upper you will need 6.8 mags since trying to put 6.8 rounds in a .223 mag doesn't work very well if at all.
I would advise you to go with ARP or Bison since they are the two of the best as far as the 6.8 is concerned.
What on god's green earth do you think your doing?