Jerry, I suspect your question is waaay over my head, but let me assure you there ain't no fleas on a .56 cal / 28ga.
I own an old "el-cheapo" T/C smoothie in .56 that shoots every bit as well as I can hold it, even better!
I have had this old beast for twenty or so years, and she gets better looking every year.
I most cases, I am not allowed to shoot her in smooth bore matches, it because she has a rear sight...that's what they say.
She does indeed have a rear sight, but she shoots a PRB like a house-on-fire, and that may be the real reason I'm not allowed to compete, but what would I know?
Ohio Joe instituted a rule, this year, in his "Smoothie Match" that allowed me to let her strut her stuff, and the old girl made me quite proud.
Insofar as shot is concerned, the best I remember the recommended load for the .56/28 is 7/8 oz shot over 65 or 70gr FFg...my regular load is 1 full oz. over 70gr FFg....
I have shot 1.25oz #6 shot over 75gr FFFg quite often, and as far as pattern goes, it depends greatly on the thickness of the OP wad....in my gun.
When using 70gr FFg, I break in half a 1/2" tall fiber Wad, when using FFFg I use the full Fiber Wad.
I always two (2) OS cards, no matter what load I'm shooting, and I NEVER Mix shot, although some do claim great results with a mixture 6's & 7's, even 7's and 8's, or even 6's and 8's for that matter, but my own experience with mixed shot has never been all that great.
I didn't answer your question, not even close, but I would suggest that if you ever get the chance to try-out a 28, or .56 cal smoothie, give it a try......you just might like what you see.
Someone with more knowledge on this subject than myself will come along shortly and give a more definitive answer...no matter the choice you make, good luck in your decision.
Uncle Russ...