The download speed may vary from extremely high to almost zero. Why?
Using BitTorrent you may download big files with download speeds of several Mbps. If you have a fast connection you can reach almost its maximum download speed. However, the download speed may also be very low even with a fast connection..
Download speed main factors:
The number of active seeders, users supplying the complete file, and the efficiency of their connection.
The number of leechers, users supplying the file in question, and the efficiency of their connection.
How much of the file the other leechers have downloaded.
How much of the file you have downloaded.
How much of the file you have uploaded.