If you transfer to a single Hard Disk Drive, the performance will always be relatively slow. If you transfer to a Raid Disk Subsystem, the performance will be (typically) much faster.
If you use a Mac Laptop with a single Thunderbolt port, using a Seagate GoFlex Thunderbolt Adapter, and a Promise Technologies Pegasus Raid system you will achieve 325 Megabytes per second actual thru put or better.
If you use a Mac Laptop with dual Thunderbolt ports, and one port is dedicated to the above raid system you will achieve 395 Megabytes per second.
(While these are realistic numbers, the above are based on our testing in our lab and your results may vary due to varying conditions.)
The maximum instantaneous transfer speed is limited by the SATA III interface, which is 6 Gigabits per second and the read speed of our SSD which is over 500 Megabytes per second.