No Ackman, you don't get it. The question asked was regarding velocity difference and that is the question we will answer. If we want to determine which is more accurate, well, we can do that too but not this time around. In order to do that, I would have to build a 223 on a platform which would be sufficiently accurate to show the difference and I'm not going to spend that kind of money on this exercise. Because of the vagaries of rifle building, barrel performance with use, and the effect of weather on performance of rifle and shooter, a single barrel is not sufficient to determine accuracy capability with two cartridges.
Back in 1978 I had a 6x47 with which I won all sorts of hardware and even prize money and merchandise in registered benchrest matches. It was a heck of a shooter and treated me well. Of course, at about that time, the 6mm PPC was coming on and I couldn't leave that six by alone so I set it back and chambered for the PPC. It never did shoot as well as it did as a 6x47. Now, while this was certainly the case, I would be a complete fool (some plainly think I'm already there anyway!)to claim the 6x47 was more accurate than the PPC. Indeed, my other rifle which was a PPC won even more for me than did that old 6x47. The point is, it takes much more than a sample of one to prove the accuracy potential of a cartridge. Proving a velocity advantage though, mandates the use of a single barrel to be in any way valid.
As I said, this particular barrel, while it looks pretty decent, may or may not shoot all that well with either chamber.
What's more, I don't really care. The purpose of this particular trial is to determine the velocity increase possible along with other potential advantages and this I will do.

I'll tell you a little story regarding velocity, case shape, and accuracy. The cartridge this time around was the 270 Winchester and the rifle was a Model 70 of about 1986 vintage. The owner worked up a load using a 150 grain hornady bullet which he could drive at just over 2900 fps. Accuracy was great with five shot groups of 3/4 or less being fairly common. He wanted more speed so I chambered it for the 270 Ackley. He could now reach 3000 fps but accuracy suffered unless he dropped back to that same low 2900's level. The next chamber was the 270 Gibbs. This got him up over 3050 but with the same accuracy results. For the final chamber, I had to set the barrel back. I did so and opened the bolt face to accept the 270 Weatherby for which the barrel was now chambered. Velocity was now pushing 3200 and accuracy was decent at that velocity but STILL the best accuracy was at just over 2900 fps. Plainly, in this particular instance, case design, capacity, and headstamp had less to do with the accuracy achieved than did the rifle itself. Does this mean the chambering is meaningless as far as accuracy is concerned? Of course not. A sample of one is meaningless.
Another story; I once fired a match from a bench beside L.E. (Sam) Wilson. Sam was shooting his heavy bench rifle which was, at that time, chambered for the .223. His aggregate was, as I recall, in the low .190's at 100 yards. I was second with an agg which was not nearly as fancy. I shudder to think how badly he would have beaten me if he'd chambered that thing for an AI wink. By the way, we both blew up at 200 yards and the only person who shot worse than I did was Sam. By that time, he was having trouble seeing (he was in his eighties). I could see just fine but had trouble interpreting what I saw. With my eyes and his brain, I think we could have done well. Sadly, I now have his eyes and am still stuck with my brain! GD