Thank you for your post.
The data transfer of the PS3205 depends on whether you are using USB1.1 or USB2. The maximum data transfer rate of USB2 is 480Mb per second however the rate used by the 3205 depends on the sampling rate that is being used. It should not vary between modes, when used in Picoscope it data is always displayed in real time. If you are using Picolog in fast block mode then the time taken to download a full buffer and rearm can be from 300ms to one second, this will depend on the speed of the computer.
Hope this helps