Well, let me throw this out there.. .
I bought the standard Armalite M15A2. I loved it. It would shoot pretty consistent 1.5" 5 shot groups at 100 yards with me behind the trigger. This was completely stock.
I thought, boy I want it to be super duper. I paid ~$700 or so to Compass Lake Engineering to fit a Krieger barrel, match sights, their 2 stage trigger and their DCM free float tube. Now it was heavier, but I was like. . .now it's perfect. I took it out and shot 1.25 - 1.5 5 shot groups at 100 yards. Since it was an A2, I never bothered trying to scope it. Moral of the story. . .If it was to be an open sight gun, I could shoot it fine stock. I never regretted that, but always pondered it.
When I sold it, I put the ol' Armalite barrel, shortened to 17" into my new M4gery. Now, with a 1-4x scope, it shoots 1.5" 5 shot 100 yard groups.
Now, the modified gun with a Krieger barrel will probably shoot under .5" at 100 yards, but it would need a 20x or greater scope to do that.
So, if you really want an A2, IMO, any basic M2 will give you a good shooter. If you want great groups, I believe you would be happier a flat top, a free float foreend and an optic of 10x or greater.
The next level up from that would be a ground up build with a Krieger barrel, matched bolt, free float tube and a 20x or greater optic.
For maximum versitility and fun, a nice M4gery with a small optic has a large following at the local range as well as in Iraq.
Also, the spec charts were mentioned. They have there place. Some makers do not meet the mil spec details well. This is not because they are making BAD guns, but because they are making semi auto civilian guns. So, an ultimate spec rifle maybe overkill when you remove the military requirements of: full auto, swimming in mud before firing, wartime cleaning, daily sand storms, etc.
Chromelined barrel choice. . .If you will shoot crap ammo, clean irregularly or both, then it is nice. Otherwise I view it as just a nice option.