I just did a 2 day Rifle skill builder at Front Sight and had a great time.  I am using a Bushmaster M4 flat-top upper with 14.5" barrel, permanent Phantom FS, and Aimpoint Comp M2 with ARMS cantelever mount.  While the Aimpoint excelled at 75 yds and under, I also found I could use it at extended ranges.  We went to "Sniper's Point", which overlooked a canyon.  Steel silhouettes were placed at various unmarked ranges out to 540 yds.  Quite a few of them were pretty difficult to pick out of the brush, etc.  

I hit every plate on the first shot out to 450 yds.  With a spotter helping me, I barely missed the first shot at 540 yds, but did hit it on the 2nd and 3rd shots.  I have to say that I was truly amazed that this rifle and optic combo was capable of this level of accuracy.  I'd still like to get an ACOG, but I can live with this.

[;)]

I liked my ACOG, but seemed to be faster with an Aimpoint at short to medium ranges.  I was actually more accurate with irons than either of the optics.  So I sold the ACOG, and now rely on a combination of the Aimpoint and irons.