The heavy load you describe in a 10 gauge is just going to feel differently, because of the greater Area of the breech of the gun, than a heavy load in a 20 gauge gun. Felt recoil is just that: Something you feel, as opposed to some measured number on a chart. Since I can't " Feel " the same way you do even shooting the same gun with the same load, I can't answer the questions.
You have received very good advice about loads for Turkey and references to Bob Spenser's website, Black Powder Notebook, for extremely good information on how to load these guns for game. You have gotten even better advice from the members here.
Now is the time to take all this advice, print it out, so you can re-read and digest it, along with the VM Starr, and Bob Spenser articles, along with anything else you have come across concerning loading and shooting Shot charges in a BP shotgun, and then go to the range and do your own testing. Be not so proud that you refuse to admit some idea you thought was correct turns out to be wrong for that gun, with those loads, and you won't go wrong very far.( HINT: Its okay to cuss when you discover that you were wrong.)
The light loads mentioned work well even in a full choked barrel. Choking a barrel only EXTENDS THE DISTANCE that you can have a good, dense pattern to insure a clean kill if you do your part of the job. Because the Round ball and pellets have such lousy Ballistic Coefficients, all that extra velocity you put behind them at the muzzle is lost in the first 20 yards. If a bird is within twenty yards of you, when you shoot, YOU DON"T NEED A HEAVY LOAD. ( Check the tables in the Lyman Shotshell Reloading Manual to see down range pellet energy, velocity, time of flight, and drop at 20, 40 and 60 yards for various velocities.)
To increase killing power, use a heavier shot size.
I use #5 shot in my black Powder shotguns, when #6 shot will do in my choked 12 gauge for the same birds. That is because the choke gives me more pellets on the game at longer distances, insuring that the bird is hit with enough pellets to make up for the smaller individual pellet energy of the #6 shot. But, #5 shot also works well in my full choke 12 gauge gun, not because I have more pellets hitting the bird( fewer pellets strike the bird at longer ranges), but because the pellets that do hit the bird are heavier, and retain more energy down range.
