I have 223 in a 10" and it is one of my favorite barrels, and most accurate. That said however, I cannot say that it is pleasant for bystanders or neophite shooters. My first hand loads for it and also factory loads provided much blast and flame that never failed to get comments at the gun range. Quite a few years ago I took advise from someone on this board and started loading lighter bullets (35 and 40 grain) ahead of IMR-4198 and that really cut down on the fire and brimstone.
So far I have not been tempted to try it in a 14" barrel, mainly because I'm partial to the shorter tubes. Also, I have 14" barrels in other calibers like 6mm TCU and 7-30 Waters to play with. I'm sure that in a 12" or 14" barrel, the 223 is everything it is in a 10" and more. It's a great caliber!
Curtis