A 100mpbs line to the internet is going to cost >100 dollars a month. You can have as fast of a local network as you want, but it ain't gonna speed up your internet. And you also have to consider that when downloading something, your download speed is only going to be as good as the upload speed of whatyever you are downloading from. For example, if you are downloading the latest web browser from mozilla, and you have a max of 5mpbs and they only have upload of 100kbps, the most you are going to get is 100kbps download from them.
Paleoconservative and proud