Terminal Performance, by whichever name , and whichever measure . Always rightly of interest , never reached a consensus definition . Never reached a consensus ranking either by caliber or specific load . And not insignificant number of observers/ commentator insist that differences only exist between broad categories, or even no difference at all between any caliber at all .
Disclaimers out of the way , my takes and observations .
There are differences . Albeit among ( duty / defensive calibers, using what l consider top performing loads ) , the differences can be small enough to not be a big deal . And individual Loads of say 9mm can overlap with certain individual loads for say .40S&W. ( Other calibers similar situation ) .
It is my * opinion * ( but l can make good argument ) , that many , if not majority , of users / PD selected the less than best choice of bullet weight for .40 .
From the experiences of " urban medium " size PD of my intimate acquaintance , and my digging into available testing, l can point to a handful of 155 / 165 gr duty loads ( that l believe ) to outperform any 9mm duty load .
[ No , l'm not saying good 9mm loads suck , or might not be rational choices to use / issue . I have no issue saying that good 9mm can be "plenty good " , or carrying 9mm . But claims that 9mm is "Better" than
40 , 10 , .45 , .357 , etc irk me .]