The K in 53K modem stands for Kilobits per second, whilst Limewire counts in Kilobytes per second.

And since there are eight bits to a byte, then a 53K modem has a maximum throughput of about 6 or 7 Kilobytes a second, and sice it is two way, then 3k is a reasonable number.

I hope that explains it and makes sense;

SkeletonKeys