(I don't have a ton of laptop experience but have looked around a little)
Again I know you want a laptop, but personally you can EASILY make a desktop config with these settings for $1,500 but you probably already know that :)
To get a 680 and that kind of specs your going to have a very hard time finding something for less then $1500 from what I have seen. I would look around at some of the boutique guys like Origin.
http://www.originpc.com/configurator...spx?SYSTEMID=3
Sadly with a 680 and 16GB of ram and a basic i5 you are looking at $2,100 from Origin.
$1,500 is going to be really tight.