[capink]

You will not import the books from the command line. You simply will copy one command to the command line, after which a dialog will popup where you can complete the process. The instructions for this is detailed in the linked post. Note that the path in the first step applies to linux and should be replaced by the path to your ramdisk in Windows, if you somehow managed to setup that.

I cannot offer any guidance on how to make ramdisk in Windows as I don't use it.

Edit: Also make sure you not using the same library you importing to in calibre gui. And that you have the latest version of the Import List plugin.

Edit2: If you cannot setup a ramdisk in Windows and want to just prevent the speed deterioration over time, you skip the step of copying your metadata.db to ramdisk, and simply copy the command and start from there. In that case, you will leave the override db checkbox unchecked, and make sure you tick the checkbox for re-initialize the db (lowering the number to 500 if you are not using ramdisk).