There's a good chance it's just dust underneath the sensor of the mouse button on your Sensei. You could always open the mouse up (screws will be under the 'feet') and give it a clean to see if that fixes your problem. You can't really get a better mouse than the Sensei, honestly. I can recommend Roccat Kone+ highly, as I have used both a lot and have zero issues with either.
Yeah, the cards themselves are all the same. I remember reading that nvidia would eventually allow custom oem coolers, but as of now they are all the same nvidia reference. I assume the only difference out-with the card, would be return/customer support of the manufacturer.