Way back in GoLive 5, there was a menu command that allows you to see an estimate of a web page's file size and how long it would take to load with different connection speeds. Does Dreamweaver have anything similar?
At the bottom of the main window, there is a line with some icons, and some values, including magnification, page size, download time and character encoding.
Go to Edit/Preferences/Status Bar to change the connection speed.
I have always found the web page file size info shown in DW to be less than accurate so I ignore it.
For an accurate calculation, I upload my pages to the web and use the Web Developers Toolbar extension for Firefox
Then Information > View Document Size.