I've been trolling with powerpro line for over 10 years with no problems. I use 80# line and it has the diameter of 14# mono (I think) and my lures goe much deeper thanks to the small diameter of the line. I use wire leaders (I fish for Muskies) and don't believe the visiblity of the line makes much diference when trolling. I do believe it makes a difference when casting. I can pull trim limbs up when a lure gets hung up. The reason for the heavier poundage is not because of the size of the fish (that's why they have drags on reels) but to keep the line from snapping when a large lure comes to the end of a cast. I cannot imagine using less than 50# line because the thin diameter of the line will cut into your reel spool, cause snags and break when your lure gets hung up. I use a very large plugknocker to get my lures back!!
Not mentioned: always wrap mono on the spool before you put your line on to prevent the line from slipping. The only downside I see to the line is it will absorb water (comes off on your hands when retrieving the reel) and your hands will freeze up from the water. Fishermen that fish very cold weather will change line during the colder weather to keep it from freezing up.