I am using Xbox 360 Wireless Gaming Receiver for Windows to play.
But I have a ****ty battery in my x360 wireless controller, so I have to plug in to the usb my play & charge kit too, but if it's plugged in my frame rate drops from 60 to 30 or below.
I have tried different usb ports too. And this does not happen in any other games that I have played.

My specs: Intel Core i5 2500k, Geforce GTX570, 8Gb RAM, Windows 7 64bit
I'm using nvidia's 314.21 beta drivers.

EDIT: Now it seems that if the xbox wireless receiver is plugged in it drops fps and it drops even more if I connect the play & charge kit. What the hell is going on ?