NATO, if they really are considering a change, oughtta stick with the 9mm (M882) FMJRN. Its higher velocity and narrower cross-section give it an edge over the .45 Auto in penetrating the heavy uniforms and gear worn by opposing forces. After defeating that stuff, it's all about shot placement in the rare occurences where a soldier most rely on his sidearm to protect himself.
If you buy into the M&S OSS books (I, for one, do not), their "stats" (if they really aren't contrived) demonstrate very little difference in effectiveness between the 9mm FMJRN (58-70%) and the .45 FMJRN (57-62%).
Might as well stick with what is in the logistic pipeline.