Between 22bra and 22xc arent you talking a difference of 20gr in powder capacity?If you buy the expensive MDT mags they work fine. If you want to feed from a mag and you want to have the total easy button go to the 22 XC. It's super easy to tune you can shoot it fast or you can shoot it slow and it is made to feed from a magazine. None of the other cartridges are going to feed as well as the 22 XC.
I've shot both. I can't say the 22 BR ackley will out shoot the 22 XC. They are very close. Aside from the extra grains of powder the 22 XC actually has the advantage to the hunter because TUBB always has brass, and his current price is $82 per hundred for both primer types. Getting 6BR brass right now is pretty slim unless you're already set up.
In a benchrest competition that 22BR Ackley might shoot smaller. I've never shot them head to head but that would be an interesting contest. They are both really great and I love them both. I'm selling a lot of 22 stuff right now simply because the bullets are available. A lot of people are opting for the 22 XC and the 6XC simply due to the availability of brass.