Abe, sorry to question your post but I dont get where you get your calculations from. The 20Mbps broadband refers to 20000 Mbits, transfer rate is calculated in MB which are megabytes of which there are 8 bits to a byte. So if your 20Mbs broadband was working on top notch you would be getting a transfer rate of 2.5MBs, that is is 10Meg file in 4 secs, a 100Meg file in 40 secs and a 1000Meg file in 400 secs which is 6.666 minutes.
Whilst I have been working out my calculations I have downloaded a 701MB file from
Broke Straight Boys with the following results:
Film Leon/Gino 25 aug 2010. Windows Media file HD version at 701mb.
The file took me just over 12 mins to download and my average transfer rate according to the box that comes up at the end was 0.95MB. .95 times 8 works out at 7,6Mbs bandwidth, which just about correct for my broadband line. If your 2.5MB line is up to speed then it will take you 280secs or 4mins 40secs to download the same 701mb file.
Hope this helps and btw I am in England.