Lt. Col. Plaster spoke of this at the NRA Conv. "Winning the Sniper War In Iraq"
Most Chechens, Taliban, Al-Quaeda, that flooded Iraq after our Shock & Awe, use 4X scopes,... rule of thumb, gets accurate hits at 400 meters. Beyond that is 50/50, based on shooter skill and equip. It's a hit or its not.
Our troops, prefer 10X optics, at long range, and a superior round in the 7.62x 51, to get effective kills out to 1000. The AR's, with 18" and/or 20" barrels have "probable" ranges covered to 400-600yds, but house to house is the most effective.
The AK, is a up and close, Katy Bar The Door, urban assault rifle. Period. Long range accuracy was never really considered; within 100yds. is a problem for those on the receiving end.
But remember, the AR is "finicky";...... twist, bullet weight, smaller bullet, conditions, let alone the shooters capabilities, all play a role. While the AK runs on 20 year old handloads, and filled with sand.
The up close house to house platform for the AR has merit. It always has. Range, and shooting beyond 250yds, + brings a lot of variables into both. Edge goes to the AR for distance, but AK has the ability, at close range, to just not stop firing.