When you add weight to a Benelli shotgun (side saddle, mag extensions, etc), you usually run into cycling problems. The Benellis are INERTIA operated shotguns and use the inertia from the recoil to cycle the action.
That said, I think with a Super Black Eagle firing Magnum loads, you will be OK with a mercury recoil reducer.
Porting helps with recoil somewhat, but it really helps tame muzzle climb.
Try the mercury first, then add the porting if you want more.
I'd also consider a top notch recoil pad.
Thanks,
Lee