You can kill birds with both O. K. ?  In order to maximize pattern coverage and have very lethal shot energy at 40 yards you just can't beat the Fed HW #7 load for 20 gauge. You only have 1.5 oz of shot in the 20. 
Fed HW weighs 15 g/cc while the Mag Blend shot are 12g/cc or 13g/cc at the most. Why use up space with #5 and #6 shot when the smaller #7 shot could be used? 
As for the FC wad issue the 20 gauge shells work for SSX, GSE,  SumToy, Rem SF, Carlson, Trulock chokes among others.