http://www.twothirds.org/caad4-geometry.pdf

The 4 and 5 had the same geometry. The biggest difference was that the 5 was the first integrated headset frame for Cannondale. No issues. It was a pro frame as your photo shows. The bike before it the CAAD4 was the first "hourglass seat stay" bike. Probably a 2001 if I recall. The chart I linked has a 2006 on it, but that was from the archive, not the frame date. If you are in possession of the frame you can check the serial number. Here's how to read it:
http://www.vintagecannondale.com/info.html

There was a short lived CAAD6 then the really lightened up the frame with the Optimo CAAD7.