I have shot 3/4 oz in the 20 for many years. I have used the regular WAA20 clone wad with 16 gr Unique in a AA hull.
Now, Claybuster has their 3/4 oz wad. It's all one needs in the 20. Might go 11/16 oz and shoot these on our Subgauge course.
I have tried and am loading 3/4 oz at 1250 in the 12 ga. With MOD chokes, this load will seal the deal on most Sporting and all Skeetie targets.