November 12, 2005My guess is the firmware on those old modems was simply set to limit the bandwidth. As long as local saturation doesn't prevent it, a lot of these things can be set to go up to 10mbps...and even higher in some cases.
You have to keep in mind that the speed tests aren't really indicative of real world download speeds. For the most part your connection will only be as fast as the slowest link between you and whatever site from which you're downloading.
All that said, if you want to play, I'd recommend dslreports.com or testmy.net.