So far, the best combo I've seen in my 870 has been an Indian Creek .665 and 3" 2 Ounce Hevi13 #7. 294 in 10" at 40 Yards at 90 Degrees with a 3" shell.
3" Hevi13 6's, 3" Magnum Blends, 3" Winchester XRHD 6's, 3" Winchester Supreme HV #5 Lead, and old 3" PMC Copperplated Lead Turkey loads have ALL given solid patterns through the Indian Creek .665 in my 3" 870.