If you like Remington 870's (like I do) and want a dedicated slug gun, I would look into the new 870 sps super slug. It comes with a heavy barrel for better accuracy and less recoil. I have a 870 express with 23" rifled barrel and cantilever scope mount that wears a Nikon Prostaff 2-7 x 32mm scope that is not a bad set-up, but does have a pretty good kick. A 20 gauge is actually more than enough for deer.

http://www.remington.com/products/firearms/shotguns/model_870/model_870_sps_superslug.asp