Ok....Heres my take on the debate...Take it or leave it. I own both. I have carried a 642 as a back up gun for 11 years. Every day. Often dropped in my pocket for a quick trip in town (I do not live in a high crime area) I have carried a PM9 for several years as an off duty gun, in my right front pocket.
I can shoot the PM9 more accuratly.
It carries more rounds.
Its easier to reload.
Its been utterly reliable for well over 500 rounds.
The 642 will remain my choice as a back up gun at work for one reason. Utter reliability. I envision the need for a back up gun being a very close up, dirty affair. Limp wristed, one handed, contact shot, rolling around in a parking lot, weak handed, possibly injured. No matter what state that little revolver is in, I am certain, it will go bang. Accuracy, though good, is secondary. If I need to shoot an armed robber across a resturant, If somebody were holding my kid hostage, I would rather have the PM9. There are no absolutes....make your decision based on all the scenarios you can envision and know, the fact that you have decided to carry something you are comfortable and proficient with puts you way ahead of the game.