Guyon, the same load you were using would be fine fired from a 10 lb shotgun. Bet yours weighs around 7 1/2 lbs.
Fred Kimble, market hunter and the supposed inventor of choking, advocated using 1 1/2 oz of shot from a 6 gauge like his.
Even in the days of my youth, loads ran under 1 1/2 oz,including goose loads, for 12 gauges. The increasing dependence on bigger loads has turned a reasonably heavy and suitable 12 ga shotgun into a overly light(for the load) flinchbuilder. My pre steel goose load was #3 shot, 1 3/8 oz, and lots of Canada geese could attest to its effectiveness.
Got some with a 16 ga, using 4s or 3s, but I had to have them close over the dekes.
Maybe 8 years ago, I did a lot of patterning to find the best turkey load for Frankenstein. The best patterns came from the Remington Duplex 4/6 loads, a 3" mag barnburner that rocked me pretty good.
Out of 5 loads I tried, the second best one(about 3 pellets less in the turkey target) was a 1 1/4 oz pheasant load, with hard shot and a 2 3/4" case. The Law of Diminishing Returns governs how much lead one can squeeze through a 12 ga tube at a time. And that's with Frankensteins' long forcing cone.
And the question more folks need to ask is if the bigger loads kill any better. The answer is yes, sometimes.Maybe.
It's not how much shot goes through the bbl,it's how much ends up in the right place in the target.
Long shot columns tend to deform more shot,both numerically and percentage-wise. If it doesn't hit the target, it's useless.
The More Is Better Principle is unreliable when it comes to shotguns.
If I were to set up a heavy waterfowl shotgun now,for $%^* steel shot, it'd be a 10 lb gun, either 12 ga 3" or 10 ga 3 1/2".