I did some tests on this very subject a few years ago.
Using a Remington 11-87, 12 gauge with a smooth bore, rifle sight barrel and a scope, using the Rem Choke rifled choke tube.
With sabot slugs it shot about 4-5 inch 100 yard 5 shot groups. If I put in a smooth choke tube, either IC or MOD it shot sabot slugs into about 2 ft. groups.
With an IC tube and standard rifled slugs, it would shoot 4 inch groups.
I never used a fully rifled barrel with sabots myself, but have heard mixed reviews from my shooting buddies. Anywhere from one ragged hole to 3-4" at 100 yds. These last results are unverifiable by me, only gun store conversations.
My only problem with rifled barrels is that you now have a dedicated sabot slug only barrel. I much prefer rifled slugs through an IC choked smooth bore barrel. They are accurate enough for me, and the ammo is cheaper and easier to find.
I once fired a 6 1/2 inch five shot group at 200 yards with a Rem 870 20" smooth bore barrel, with a 3-9 scope on it. Honest!