CAliber is secondary to a point. .22/.25 vs 9/40/45 for example.
The real quesiton is reliability of stopping. And in that area, bigger is generally better.
9 v 40 - likely no/little diff
40 v 45 - also likely the same
9 v 45 - maybe some, but possibly marginal difference. Gotta love 45 though! That said - I generally prefer 9
but .25 vs .45....there WILL be a difference there.
You have to run the experiment enough times to rule out luck, obviously vital hits etc.