I tried every sabot slug I could find in 2 3/4" and they all grouped like yours,except for the "copper solids",just over 1", but at $20 for a box of 5 that got expensive real quick. The next closest was the Whinchesters at around 2.5" @ 100.
Savage says to use 3" Win. but my shoulder doesn't like the magnums so I'll setlle on the 2.5" groups. I don't have many shots over 60-70 yards where I hunt so I called it good to go.
Should have saved close to $800 (gun,scope,rings bases) and stuck with my Ithica 37, 16guage with the Foster slugs, shot about the same at that distance.