My short answer is "yes," it usually matters.
I suspect, with a correctly designed experiment, it could be shown that it does not matter on paper. That's because in a laboratory setting, such as shooting patterns on paper from a benchrest, it would be possible to eliminate virtually every other variable but bore size. But who would be interested in such data unless it could be related to the field. And that's why I say it "usually matters."
Once you move to any sort of real world scenario, be it the target field or the game field, a plethora of other variables having to do with the shooter and the equipment overwhelm any attempt to isolate the bore size variable. It matters because, typically, no matter how hard competitors try to make it so (and no hunter would want to), a 20ga gun is not the handling equal of 12ga gun.
The clearest opportunity for that would be on a skeet field where a tubed gun would come the closest to using equipment that was identical except for bore size.And since it has been demonstrated countless times that 1/2 ounce is sufficient to break 100x100 skeet targets, how many would have to be shot at with 3/4 ounce before one could believe .630 vs .730 can make a difference? Makes my head hurt to ponder it.
I'm gonna leave now and go separate the fly poop from the black pepper.
