On a 750kbps service, you should be able to get a maximum of something like 93.75kb/s, although that depends on loads of other factors. You say that 2 files were downloading at 80kb/s?
Which download accelerator were you using? How were you getting SP2?
You will often find that software misreports the speed of a download, normally by showing speed decreasing slowly, whereas is may have 1/2ved the speed straight away.
As a test, see if you can get it to happen again, and then double click on the two blinky blue boxes in the system tray - that shows you the actual [or as near as damnit] internet traffic, and expect the 'Received' never to jump more than 90kb in a second. Sometimes it does, you will normally find that the next second takes longer to appear

I once pretended I had ADSL with someone on the net when I had 56k.....basically you pause a download [I think I was using DAP], for about 15 seconds. Then, when you restart, it tends to claim it has downloaded about 100kb in the second before, and gives all king of crazy figures!
BarcrestBenito