Is this
9x17mm .380 auto to us
9x18mm Makarov
9x18mm Police (9mm Ultra)
9mm Browning Long (9x20mm Browning SR)
9mm Glisenti
9x19mm Parabellum (9mm Luger, 9x19mm NATO)
9mm Federal
9x21mm IMI
9x21mm Gyurza (9x21mm SP-10)
9mm Action Express (9mm AE)
9x23mm Steyr
9mm Largo (9mm Bergmann-Bayard, 9x23mm Largo)
9mm Super Cooper (9x22mm Super Cooper)
9x23mm Winchester
9mm Mars
9x25mm Mauser (Export caliber for C96)
9mm Winchester Magnum
9x25mm Dillon
9x25mm Super Auto G
9x30mm Magnum (9mm Dillon Magnum)
The .38 Super, introduced in the late 1920's. Higher pressure and velocity than the parent round, the .38 ACP. It was used in Mexico a lot because it wasn't a military caliber. Civilians were not allowed to own military caliber handguns.
I have an X5, it performs really well, but the lack of parts, super-expensive mags puts it low on my list. It is also too pretty and expensive to subject to the customary holster marks, scratches and dings sustained by other pistols. Without those, one can not be proficient in it's use.