What Jon Jon said.
You always need to train heavily with a new gun platform to become proficient. However, it's important to have a gun that fits your hand.
I would recommend a small 1911, but the Springfield EMP is only 2oz lighter, and the Kimber Ultras with aluminum frames are only 3oz lighter. Compare that to an M&P9c, which is almost 7oz lighter. You lose almost a half pound of gun weight by going to a subcompact polymer gun. Either way you go, you will lose ammo weight by going to smaller mag, and that does make a difference.