D600 speed with LR4 through USB

The other downside of hooking the camera to the computer is the extra wear and tear on your camera battery, I have always used a card reader for off loading a card, does  your computer  have USB2 or 3 sockets ? If 3 I would suggest a multi card USB3 reader, I have the Sandisk version  ( only because that was the only one available locally ) but there are others, my 16 GB 400x Lexar CF cards take approx 5 minutes to offload fron the card via the computer to an external HD, I just make a folder for them  then open them in Bridge for initial culling then PS for editing, old school but it works for me