I had a 6mmAI for quite awhile. Mine was built on a 40x short action and had a 26", 12 twist Hart barrel.
I had no problem killing varmints out past 600yds with this rig and 70gr B-Tip bullets. Even the 55gr bullets shot very well and I killed hundreds of groundhogs with it.
I had a tight-neck chamber. Presumably, if you tailor your ammo for the tight-neck chamber properly, you will get greater consistency in the ammo, cases should load more concentric (better chamber fit), accuracy should improve and cases should last longer. I favor tight-neck chambers in all of my precision long range rifles. In production grade rifles or for use at moderate distances the tight-neck would be a useless waste of time and effort, IMO anyway.
Although a target/varmint rig is normally unsuitable for use as a deer rifle, the 6mm is certainly plenty of cartridge.
Here is a link to a site that will give you lots of insite on the 6mmAI.
Mike's 6mmAI Page