A point to consider are a few of the newer, ultra fast rounds like the 5.7mm from FNH-USA.
A 5.7mm pistol was used by the US Army major in the tragic Fort Hood TX spree shooting a few years ago. To my limited knowledge, the US Secret Service also packs the compact 5.7 P90 SMG to deal with any threats that wear body armor. The standard sidearm remains the SIG Sauer P229R DAK pistol in .357sig. The USSS has used the .357sig since the mid 1990s.