I think the Benelli Supernova's also come drilled and tapped for a rail.
I went with a Speedbead and a Burris FastFire III (3MOA) dot on my slug slinger as mine wasn't and we also shoot some turning targets with slugs over here
I do like the speed and how intuitive the red dot is. But as others have said, a scope is better in low light. (I went for a low power scope on my .44 mag lever action as found it better for that - interesting comparison between straight walls and slug guns)
In terms of ammo: get Brenneke type slugs not Foster would be my advice
Scrummy