Bear in mind that there are several critical issues that can impact your transfer speeds. Cable modem systems are more vulnerable to some of these issues than DSL or other directly connected systems. Of particular interest to those sharing files is the impact of aggregated upstream capacity limits. Not only can this trash your upload speed, it can also have a significant impact on your download speed.
One of the very best resources on this subject is the Navas Cable Modem/DSL Tuning Guide (
http://cable-dsl.home.att.net) and you may find the section on asymmetry (
http://cable-dsl.home.att.net/#Asymmetry) to be of particular interest.