Sigh. The M4 doesn't suit Pakistan's Climate nor terrain. Nor does it's cartridge suit the role. The 5.56mm is made for wounding, so the enemy has to spend more resources on getting their soldiers out and treating them, which also in turn affects enemy morale and making it easier for logistics to bring more ammunition to the front. The enemy we're fighting now aren't a trained army, nor do they have to care for their wounded, nor do they use the 5.56.
The M4 was built for Urban warfare more than anything else, so the SSG should use M4s when in Urban areas, but use the AK series while fighting the enemy in forests, mountains and deserts. They won't need to bring much ammunition since they can pick it off dead enemies as well.
(Added bonus if the SSG use 7.62 Hollow Point since the Insurgents don't use any armor. The Hollow points are going to give them a new definition of pain)
Effectiveness > Looking cool
Almost everywhere the 5mm went against the 7.62, it lost.
In Vietnam, the US army started to use the 5.56 rather than the 7.62x51 against 7.62x39 and 7.62x54R, while fighting against an insurgency.
In Afghanistan, the Soviets just adopted the AK74 which was in 5.45x39 and went up against an Insurgency which used captured Arab AKM and AK47 7.62s, courtesy of Israel for sending it to them through us.
Then the Americans came and fought the Taliban with 5.56, and even after a decade and half of full military onslaught the insurgency still remains, stronger than ever.
Perhaps this is so because 7 is a lucky number?
Jokes aside, in my opinion the 6.5x39 Grendelski is the best assault rifle cartridges that Pakistan should go for. It's the best of both the 545 and the 762 combined into one cartridge.