THe 40 is a great pistol round. It is my favorite, and I carry one almost every day. I've shot a ton of varmints with mine, from rabbits, to skunks, badgers, coons, etc etc etc. It performs very well, and I can get some good deals every once in a while on some Remington HPs.

I've never shot a M&P, so I can't be much help to you there.

My 40 is a Springfield XD Tactical model.