My 16" AR shoots the factory ammo I use with a 55gr V max at 2750fps.
My 20" AR shoots the same ammo to 2964fps.
The same 20" AR shoots the factory 53gr V max Superformance loads at 3286fps. I just experimented with them last week and got one .5" group, chronographed 5, and then shot a 1.5" group. I need to get another nice day and shoot some more to see if they shoot well enough to justify a switch. The ammo I'm using is consistently .5" right now and I won't give up much accuracy for speed.
As was mentioned above, I feel my AR is definitely at it's best inside 250yds with it's standard duplex 2.5-10x scope. 1.5" high gets me to 225yds without compensation but by 250 I'm 4" low and at 300 it's 10" low. I have considered getting a different scope for it and moving this one to my back-up AR, but haven't done so yet. This scope works pretty darn well for 90% of my calling. It's only this time of year when I'm hitting spots for the 2nd or 3rd time and running into more coyotes hanging up at 300+ yards I start wishing for more range.
I would like to try one of the Burris Eliminator 3 scopes in a 3-12x with the built in rangefinder and wind compensating reticle but haven't wanted to put out the cash. Trying to range a coyote, dial the scope, and then shoot it without getting spotted is a lot of movement to get away with. Especially since I like to move from sitting to prone if at all possible for those longer shots. Having a scope with a built in rangefinder that doesn't need dialed takes steps out of that process.