Right now, I'm downloading Requiem: Bloodymare over torrent (legal torrent, it's hosted on the game's website). Overnight it gained very little progress, with speed sticking to about 35:35 with unrestricted download and upload, using uTorrent with port forwarding. So, in order to let it run today without interfering with my mother's web browsing, I cut the upload in half (15), and now my download speed has doubled.

Is this common? Did I need to cut my UL a bit to open up room for my download?

Short answer: Yes and Yes.

Yup. You always want to limit your upload to roughly half of your maximum to keep your download rates up.

Actually you can go up to 70-75% on your upload without affecting downloads much. My max up is 512k, so divide that by 8 and you get 64K, 70% of that is roughly 45K. I set mine at 45K up during the day and unlimited over night, if I don't have anything downloading.

Yep, i have to keep my upload limit as well although my internet has pretty slow uploads incomparison to fast downloads so i can keep it at the 50% people have mentioned.

My advice is play about with the speed and watch the difference, before my speeds were upgraded i knew exactly what setting to use, though now i can upload a bit fast without affecting downloads.

I never have a problem with my Dl speeds when I allow max upload.

Course, I use private torrent sites..

I cap mine at about 100k because I have a fast connection and also because I like it when I get fast seeds, so I would like to return the favor.

It really depends on the tracker and what limits they have set...