It appears based on just raw number that I have seen that the projectile weight and velocity of the .327 Federal, at least from 4" or less barreled (and especially 3" and less) revolvers is remarkably similar to 9mm from 5" or less barrels.
That said, other than the one more round, and the moon clips vs rimmed cartridge, why might I choose a .327 Federal over a 9mm revolver?
TED
The biggest benefits that I see to the 327 fed are 1- access to multiple calibers/brass lengths (32acp, 32 long, 32 H&R, 327 fed), and frame size.
Generally the 327 is found on J-frame sized guns or the sp101, vs the 9mm being K/L/N frame or Gp100 sized.
I had a 327 for a bit its close to a 9mm. The only advantage in reality is 1 extra shot over a .357 or .38. The mulitcaliber thing is kind of useless as the other calibers are all fairly rare and expensive.