Hi dutchoven,
Welcome to the boards!
I live in a "shotgun only" area of Maryland and have the 20ga bbl. I purchased mine fron Fox Ridge Outfitters; T/C's custom shop, because they offered the bbl w/o iron sights and since I was mounting a scope on it, I had no reason for the sights.
Everyone, including myself, shoots "cloverleaf" groups at distances out to 80 yds off of a rest. (This is the limitation of my shooting area.)
I have made clean kills with my 20ga out to 119yds just this summer. <I have crop damage permits>
For my particular bbl, the Federal Premium w/ the Barnes X bullet and the Remington Copper solid have given me the best groups. I am eager to try the new Remington Core-loct that has a published velocity of 1900 fps. I found that the Winchester Supreme w/ the Nosler Partition gave me poor results, often "minute of pieplate". I am curious to see if the longer bullet of the core-loc yeilds better stabilization downrange.
You will just have to "shoot and see" which slugs work well in your bbl, but I have shot most of them out there and from my experience, the more expensive slugs shoot better.