Here's a couple of quick & dirty reads on the M9/9mm ('cause that's what it is

Not the final word, by any stretch of the imagination. And my preference is ... ???

http://www.sightm1911.com/M1911vsM9.htm
http://www.findarticles.com/p/articles/mi_m0BTT/is_158_26/ai_86704766/print