For Web browsing, past a certain point increases in download speed don't make even the tiniest difference. The limiting factors become the speed of the Web server serving the site, the bandwidth of that server, and the speed with which your computer can render HTML/CSS.
Where high speeds really matter is when you're doing large streaming downloads (for example, movies) or when you have multiple tasks all using Internet bandwidth at the same time (multiple computers, perhaps, or maybe one computer doing a download, browsing the Web, fetching email, doing an upload, and playing a game at the same time).
I have the fastest tier of residential broadband available, because I have several computers using this connection (including a server) at once and because I often do very large uploads. For most people's use, the broadband I have would be overkill.