Hi,
I'm new here so probably not much respect but I'm going to stick my 2 cents in anyhow.
Get a Nikon Slughunter. You can't go wrong with Nikon glass ever.
I have a 3-9 x 40 slug hunter on my 870 and since I wear glasses and have poor eyesight, the 5 inches of eye-relief is sure nice. Its a darn high quality unit that sucks in the light.
Mount it with a pair of weaver grand slam steel rings and you'll be all set to go.