Although you could try to do this via network simulation or downgrading your bandwidth, I recommend doing it on the client instead, using your webpage editor Dreamweaver, or some shell scripting.
To do that in Dreamweaver
Select Edit > Preferences (Windows) or Dreamweaver > Preferences (Macintosh).
Select Status Bar from the Category list on the left.
Select a connection speed with which to calculate download time and click OK.
To do it via math, calculate total page sizes and embedded images, script, etc then compare across different speeds.
Understanding the user’s perception of “fast”
When thinking about speed of internet connections, remember that speed (latency) and bandwidth (breadth of the pipe) are two different things completely. You should consider both in building webpages, including browser render times.