BTW, it's faster to ingest each disk individually rather than selecting them all at once. Selecting them individually and starting ingest will allow concurrent downloading while selecting them all at once will result in sequential downloading (i.e. one disk after the other). Hope that explanation made sense.
It will also depend on the speed of your memory cards. If they're really fast, then throughput to the computer may max out at two cards... but if you're stuck with slow old cards, downloading them concurrently is about the only way to make downloading more efficient.
Since my laptop has two USB ports and one FW port, I attach a card reader to each (the small black Lexar to the FW port and Sandisk Image Mate USB readers to the USB) and go from there... not as neat and tidy as the Lexar Pro readers, but cheaper and not a bulky.