What affects transfer speed when shooting tethered?

When I am shooting studio portraits tethered to a Macbook Pro, the images transfer slower than I would like them to making the process a bit of a pain. I have stopped doing it but would like to go back to using the bigger screen if it's possible to speed up the process.

I am using USB cable from 5D MkII to the computer with Lightroom 5. Is there a way to make things faster and smoother? Would an SSD drive make a difference here? Does it make a difference if I'm using an external hard drive instead of the laptop hard drive?

Your limiting factor is probably the camera's USB port. For an example of the difference that can make, try comparing file transfer (download) times for files from your camera direct to the computer, and those same files with your card in a good card reader.

If you have a fast CF card your limiting factor is likely your camera. A good USB card reader would certainly speed up transfers especially if you have the option of USB 3.0.

An SSD really will not make that much of a difference to transfer speeds unless you are buy the most expensive memory cards out there. Most modern hard drives can write at 100-170MB/s+ consistently which will be faster than the large majority of CF cards out there. Depending on the age of the laptop hard drive an external hard drive may be slightly faster but its unlikely to offer a significant performance difference unless the laptop hard drive very old.

A USB 3.0 card reader will benefit you more than an SSD will in terms of performance as well as being significantly cheaper.

As a side note an SSD is a great PC upgrade that will make everything feel much more responsive and assuming your processor is not the bottleneck will speed up batch file conversions as well.