What is the smallest, useful handgun for discreet CCW?

[Pappabear]

I have an M&P 340, but unless it was close contact (10yards or so) I would be afraid to squeeze. I think stats show most situations are inside of 10 yards? But this thread reminds me to go practice with it. Because in comparison, I'm not nearly as good and it's getting HOT

Then I move to XD40 sub-compact from a size stand-point, which IMHO, with that thickness why not carry the admirable G19- so I usually do that.

I am very interested in the M&P single stack 9mm coming out. I don't understand why more companies have not done this to compete with the Kahr single stacks that get so much play with those (1942 eastern Germany like) triggers. I know people love those Kahrs, and they get rave reviews, but I think i would prefer a single stack M&P.

It's girth that has made Kahr millions, God love em for pushing the issue.