Fernando, I look forward to reading someone's answer ( who's smarter than me) to your movie download dilemma.
My download issue was caused by Time Warner's daily (3:00AM) updates to their componets. Occasionally, (1 in 500 according to one of thier technicians) a cable/internet modem is "disturbed" by this update.
So even though we were paying for 40 mgps download speeds with our internet service we were getting 484 kbps download speeds for weeks. Time Warner does not test thier equipment's speeds nightly, even though, I believe it is technically possible and practical with their existing equipment ( obviously a software change would be necessary).
By "resetting" the modem (ie. unplugging it from it's power source for 10 seconds) the "problem" was resolved.
I used Speedtest.net to "ping" Time Warner's server and then called (ie. Calmly but obviously furious) Time Warner with the results!
The moral of my story is: test the speed of your internet connection and contact your ISP to get the results for which you are paying! If my story helps you, go get 'em...and get a discount!
I look forward to reading about the underlying cause of your movie download speeds.