My A4 is mounted with the Leupold Mark AR 3-9. Its calibrated turret for 55-grain .223 loads is very slick. I've been very happy for it as a general-purpose rifle. I even used this configuration during a 4-day Practical Rifle course at Front Sight, including using it to win the shoot-off at the last day.
At 3x, it is very respectable for 25-yd shot placement on targets that are expected. It may be a different story when you would prefer to keep both eyes open for scanning.
At higher-power and with the turret calibrated, it really makes for a one-rifle, any-range package, but yes, something else would be preferred for CQB; this being a 20" HBAR anyway.
My CAR has a Trijicon ACOG Reflex on top of the carry handle. I put a cheek piece on it, but it still takes some getting used to. I already know I do not like the Reflex on the A4 with the front sight tower permanently in the way. I will probably get rid of the CAR in favor of an M4 or different platform, maybe just stick with the M1A SOCOM 16, but then it has a scout scope with 2.5x, so that still takes away from the CQB a bit.
Then again, I'm not storming buildings for a living, either. And my Remington 1100 will do nicely if I ever get it back to working (thread on this forum about the fore end not fitting...)