870 Rem 26" barrel using Hevi-13 #7s most chokes in the 560-565 range are going to be very acceptable and 570 not that bad either. The newer H-13 in 5 /box #6s are getting good reviews in the 570 choke. I concern myself with what these patterns look like at 30-35 yards more so than 40 since I rarely shoot that far even with the 12 gauge.
If you use lead only then a 560s range and Win XX #6s or Federal FC #6s and then #5s would do well for the 30 yard and under range especially.
Good Luck