I have the Rem. 870 express also tried a few set ups until I found the one I was most happy with......
Rhino choke .660 and Nitro 4x5x7 =64 pellets in the turkey target head and neck most of the rest in a 10 inch circle at 40 yards. the longest shot I have ever needed to take was at 30 yards even at 20 yards a clean kill.
When you get a chance you might want to try it. Sounds like you have a good setup.