I actually posed a similar question, on a different board, and to a few guys here. What I got, was basically that guys who could use lead used 2 3/4 loads, successfully. Few had bothered with the 3 20 gauge, prior to non toxic shot. The guys using non toxic shot seemed to step up to 12 gauge, and not look back.
For what it is worth, I patterned 3 20 gauge loads out of a Ruger Red Label about 40 years ago. The gun about kicked my teeth loose, and I found almost no difference in patterns at the board, at ranges I would shoot while carrying a 20 gauge (NOT 40 yards, maybe not 35). Loads have come a long way since I tried that, but, nobody seemed to feel the need to make their 20s into 12s, from what I could see.
I have a 3 20 gauge, left to me by a late friend. He was a hell of a good guy, but, the beavertail, white line spacers, and pistol grip make me feel a bit like I am wearing a plaid, three piece suit when I use it in public.

Post what you find out. I have no desire to repeat the patterning exercise I went through as a younger man.

Best,
Ted