Have gotten this theory from somewhere but would like your input. I've always like the lumpy idle that comes with bigger camshafts with long duration. Can you get the same effect by keeping the total duration lower and decreasing the lobe seperation to 106-110?

 

As long as the overlap stays about the same, yes. You can also get most of that effect by lowering your spark advance at idle.
There are several disadvantages to doing either, so you might want to reconsider if it's just for the sound.