The difference in pellet count for 7/8oz vs 3/4oz for shot sizes #7 through #9 is about ½ size. That is 7/8oz #7½ has about the same coumt as 3/4oz #8 etc. #7 is not always easy to find & as shot gets larger it takes more to compensate, 1oz #5 has a similar count to 3/4z #6. As to increased shot count from a heavier load taking a choke giving similar patterns for both & using same shot size the heavier load should give an effective increase in range approximately equal in proporyion to the sg roots of the charges. Thus the 7/8oz should have abount an 8% more effective range than a like choked gun firing 3/4oz.
From a pure ballistics standpoint in shoyguns the advantage will virtually always lie with the gun having the biggest hole down the bbl, "Until" that size makes it unweildy.
There can be many reasons for shooting a 28 & I would not in anyway want to discourage anyone from shooting & enjoying one. The cold hard facts are though the 20 will allways be a slightly more effective & versatile gauge.
