[jotm]

In my experience, the GPU, USB and SATA are the causes of sluggishness without CPU usage. Not sure what could be the problem with your dock - does it have a USB 3.0 controller that the laptop does not? eSata? You are 100% sure the CPU is not being heavily used by anything after first time docking?

[sebazzz]

The dock is a standard wide-connector Dell port replicator, with indeed USB, DVI connections and possibly eSATA. USB 3.0 did not exist back then.