Torrent download speeds are determined by a number of factors, so it's hard to really give a general number for every download. Usually, public places like Hongfire/thepiratebay don't have well-seeded torrents (not always the case), and the few people that do seed tend to have slow upload speeds.
More seeds means more seeds that you can connect to, which equals quicker downloads. Less seeds means less seeds that you can connect to, which equals slower downloads. Slower/quicker speeds depending on the available number of seeds is not the sole factor in download speeds, though. Leeches (the people that are also downloading the same file as you) also play a factor in this, as they're consuming bandwidth from the available seeds. Leeches can also upload (just like seeds) to other available leeches at the same time, though, if they've already downloaded part of the file that other leeches still need. Another thing to consider is that leeches and seeds can toggle the amount of bandwidth they want to spend on uploading (or downloading). So, you can cap your upload speed at 20 kb/s if you really wanted to, even if you could upload at much quicker rates.
The most important thing to consider is your ISP's connection plan's speed, and the seeds/leeches' respective ISP connection plan's speeds.
That's just my experience, though. Sometimes you'll get 80-100 kb/s or higher download speeds from just a single seed, if there are no (or few other) leeches.