I haven't shot the 5.7; but it definitely feels nice, like you said. I've got the 9mm MP, and I love it. Super fun to shoot.
Based on the ammo alone, I would go with the S&W. You can never, never, never go wrong with a .45. The 5.7 is still kind of an obscure round, and ammo may be difficult to come by down the road. The .45, however, will always be accessible. Not to mention you'll probably always pay a premium for the 5.7, making the .45 cheaper to shoot.
On top of that, the 5.7 isn't even as big as a .22 (at least in diameter).
Maybe you should just get a Kimber. Then shell out the extra cash for the .17 HMR conversion...Or maybe I'm thinking I should do that. Either way it's some food for thought.