If concealment and .40 cal are your parameters, then I would suggest getting a Glock 27 in .40 S&W, then get a Glock 23 or 22 magazine (depending on your hand size and comfort) and install a A&G Grip Spacer on it. It will give you a 'full-sized' grip, with a subcompact-length pistol for concealment. If you're wanting a subcompact grip, then just add a pinky-extension to help improve your grip feel and control recoil.
Remember...if you get a .40 pistol, you can always go back and get a Lone Wolf 9mm conversion barrel and 9mm mag and shoot 9mm out of the same pistol...but you can't go up from 9mm in a Glock.
Remember...if you get a .40 pistol, you can always go back and get a Lone Wolf 9mm conversion barrel and 9mm mag and shoot 9mm out of the same pistol...but you can't go up from 9mm in a Glock.