Re: 3 gun AR's
There isn't much a 16" middie can't do within the realistic expectations of 5.56. My GP AR is a 16" BCM. With an optics swap and use of applicable ammo (or when the new generation of 1-8X optics hit the market) it can go from CQB/urban in any lighting condition to 500 meters on torso targets.
My competition AR is an 18" Noveske. It's great, but not really the best stick for fighting inside.
The new trend of 14.5 middies have a strong following, but you do lose a significant amount of MV, which is directly relevant to terminal performance of 5.56 as range increases.
ETA: as far as holes in paper are concerned, optics will be the biggest contributor to accuracy. I have a distinct preference for quality 1X optics (or a low-powered variable with the bottom being as close to true 1X as possible) for a fighting rifle. When it comes to daylight competitions, low-powered fix magnification in the 3-5X range do very well, such as the TA11 and TA33 ACOG series. I am not a fan of the TA31 or TA01 series due to their constricting eye-relief. The addition of a 3X magnifier to an Aimpoint T-1/H-1, Comp M2/M3/M4 (or C3), or EoTech (many different models with the 1 MOA and 65 MOA halo, just different battery sources, or the XPS with it's lateral CR123 battery, or EXPS with lateral battery and built-in mount) do well out to 300 meters or so with a 100 meter zero as long as you know your holds past 150. Beyond 300 is do-able, but requires many more sighters due to the difficulty in obtaining hold and observing strike.