I don't know that the big hole, small hole theory has much to do with reality.
Marshal & Sanow developed data which depicts 9mm FMJ and 45ACP FMJ as roughly comparable in stopping power (I don't sweat the small % of difference). Their numbers shattered the balloons of others and the war was on.
Decades later another cop, Greg Ellifritz, has published his own numbers, using different criteria and he also finds the 45 and 9mm Parabellum are not that far apart. Ellifritz's bottom line is: For serious fighting use a rifle or shotgun.
Excerpts of Ellifritz's paper.
# of people shot - 456
# of hits - 1121
% of hits that were fatal - 24%
Average number of rounds until incapacitation - 2.45
% of people who were not incapacitated - 13%
One-shot-stop % - 34%
Accuracy (head and torso hits) - 74%
% actually incapacitated by one shot (torso or head hit) - 47%
# of people shot - 209
# of hits - 436
% of hits that were fatal - 29%
Average number of rounds until incapacitation - 2.08
% of people who were not incapacitated - 14%
One-shot-stop % - 39%
Accuracy (head and torso hits) - 85%
% actually incapacitated by one shot (torso or head hit) - 51%
Based on this study one should be prepared to need more than one round to neutralize a serious threat.