I read articles and threads on how lighter line throws lures further because of less drag but are there any cons to throwing a 2 lbs test on a Rod rated for 4-6 lbs?

Line ratings on a fresh water rod are next to meaningless. They are just a recommendation as to what the rod is good for. Underlining a rod within reason, is no problem at all. 

No problems at all. As long as the reel you're using has a drag smooth enough to protect 2lb line, that is.