IMO, this is a best choice. . .
Burris AR-536 + Fastfire 4 or 8 MOA
I have a 1-4x. It is fine, but would never be a truely fast combat optic. 4x is ok at 300 with a 1 MOA dot, but 5x would be a little nicer. Also, a quick raise of the rifle, would have me looking through the red dot. Cheek weld would be crap, but don't need at short distance.