The weird thing is that unless you are experiencing heavy network traffic (such as someone moving large files from one computer to another), I would expect ethernet to either not work at all or work as advertised. Working, but very slow doesn't really sound like a configuration problem.

When you mention how long it's taking, are you including the Rebuilding of that Database? The time it takes to do that depends mostly on the number of tracks you have and not on the connection.

EDIT: Tony's suggestion that possibly some software was installed on your computer to "optimize internet speed" or reduce pings for online gaming is sounding more and more like a possibility too.