If the .660 tighwad doesn't give you what you want, go with the .660 JellyHead. You also might want to consider the Indian Creek .665. My 26" 870 barrel shot 230 in the 10" with the 3 1/2 Magblends with the .660 JellyHead. Your 28" should even be higher. With straight 3 1/2 Hevi 7's you should be pushing 300 pretty easy in the 10"
As far as the 20 ga....my 3 considerations would be the Remington Super Full, SSX .550, and the Indian Creek .555. I shoot the IC .555 and it shoots all loads great. From Hevi 3" #7's to 3" Federal HW #7's.