Hi,
Yes the Dart is much lighter. I don't have the numbers though, but have moved one around a few times. The Dart is also a very good single hander. As for speed, the TheMightyHobie18 will probably be faster upwind due to the dart not having daggerboards. Not sure about speed off the wind.

If you would like a test ride, we have both boats in our club and we are a couple hours east of Toronto.
Dave
http://www.westlakesailingclub.com