I have a 6mm AI and am pleased with it. If you push it, the 6mm Ackley should outdo the 243 Ackley, but they are pretty similar. Make sure you get a 1-10" twist to stabilize the big Bergers. The 6mm AI is said to have longer throat life since the neck is longer. Both shoot wonderfully flat for a long ways with little recoil.
Both those would be real speed demons. I have a standard 243 win and my accuracy load gives me 3120fps with the 108gr Berger BT. 3 shot groups 1/8 MOA to 1/4 MOA at 300yds and 10 shot groups under 1/2 MOA at 300yds. I use a 26" Douglas with 1:8 twist and plan on testing the 115gr DTAC. I considered the 243AI but I figured it'd just wear the barrel out that much faster.
I'm looking at a 243 AI - mainly because of case life moreso than outright performance.
However, and not from experience, but hearsay, I've seen that throat life may apparently be better on the AI (yes it surprised me too and I couldn't substantiate it).
Also, we all know what the std 243 Win's barrel life is reputed to be, but on Jarrett's website they speak of 2000 rounds as I recall. That was by implication with 85gr bullets if you read between the lines, though.
The 6 AI has a slight advantage on power due to it's larger case capacity. However the 243 AI has an advatage on case availablity since you can easily get Lapua brass. You can neck down 7 x 57 lapua brass to get to the 6 AI but it takes more work. Both are going to be fairly hard on the barrel. The 6 AI will come close to 6-284 performace with better barrel life, it is a better designed case with a longer neck which helps throat wear on barrels. The 243 AI has an advantage in short action rifles because of the shorter case length. They both can give some problems in stagger stacked magazine fed repeaters due to the 40 degree shoulder.
Either one would perform well with 105 grain bullets and a 8 twist. However, I would venture to guess that you would probably get a few more accurate shots out of a 10 twist and lighter bullets due to the fact that fast twist barrels with slight throat wear tend to tear up bullets faster than slower twist barrels with ligher bullets and similar throat wear (This is just a thought, not tested or anything by me).
I used to re-load but now I "hand-load".
-- Well, at least I try --
I have some winchester brass that Have over 8 fireings shot on them and they're still holding up in my 243 ackley. I trimmed them back after 5 fireings. The nosler brass that I'm using now just has 3 firings on them and haven't stretched out yet.
The winchester brass was what I started with as a fireforming/work up loads scenario.
I bellieve the 8 twist or faster is the way to go for the heavier bullets. I have a 7 1/2" twist barrel on order right now for my new build. THe old one has a 8 twist Hart 26" barrel and I have 580 rds through it without any throat wear that I am aware of.
I would go with the 6MM AI and a 1-10 twist barrel. It will push the 87grn V-Max to around 3600+fps very accurately. It's an awesome cartridge it just takes a little work to get the cases formed, however, after that it's awesome. Also the 7x57 Lapua brass is very consistant. It takes two steps to neck the 7x57 down to 6mm. First you have to neck it down to 6.5mm and than to 6mm. This takes stress off the neck area. Anyhow, good luck and have fun.