I've always been told the inertia action of the M2 Benelli was faster than the ARGO M4.
My former PD Sgt (now deceased) had an M2 shorty and loved to show off how he could empty the gun (6+1) before the first ejected round hit the ground. That is hardly scientific though!
I own an M4 and it is faster than I am.
This thread is like comparing a semi auto pistol to a revolver. Any idiot can miss faster with a semi auto pistol than a revolver. But when you compare IDPA times the revolvers are just as fast as the semi autos. The same thing applies to shotguns. The pumps are just as fast as the semi auto shotguns at actually hitting a target with a full power load. The muzzle flips just as much with a semi auto as a pump. It's more about the shooter than the gun.