FWIW I own 3 870's 2 Supermags 3.5" and one 3" mag
Have 21" and 23" and 26" length barrels for all.
Hands down the 26" barrels Patterned best and reached out the farthest with Winchester LB
XR shells
Ended up being the same for my Benelli SN and Mossberg 835.
All wear 26" tubes
Tried Indian Creek, Carlson's XR and factory Xtra full tubes and surprisingly the Carlson's patterned the best.