I've read the documentation and FAQs and understand the limitations on download/upload speeds, but I can't figure out why these speeds vary so violently.

I've been trying (unsuccessfully) to download a large mpeg for the last few days. I've seen download speeds vary from 0.5 KB/s up to 30.0 KB/s and back down again in less than 60 sec. At the same time my upload spends remain a fairly consistent 3 to 5 KB/s.

What causes this vacillation?

Anyway to improve download speeds?

Happy Thanksgiving.