I received an answer from Support about the upload speeds of PP:
A general rule of thumb for your maximum transfer rate is to divide the Upload speed where Pogoplug is installed by 8. In the case of a typical DSL connection with a maximum Upload rate of 512Kb/s, the maximum transfer rate would then be ~512Kb/s divided by 8=64KB/s. Check out this old but good link which explains transfer rate.
Is there a way to change this? If you do the math 1/8 of your upload speed is = .125 or 12.5% of your connection speed. Dropbox's default is 75% of your connection speed with an option to remove the limit: https://www.dropbox.com/help/26/en