For kings I troll 1.8 - 2.2 mph using my sounder as a guage (water speed under boat). For blackmouth...the same but usually the high end of this range. Finally for silvers anwhere from 2-4 mph. I don't usually refer to my GPS speed since ground speed may or may not have anything to do with how fast my gear is moving through the water. I use the angle of my DR wires as a gut check on my speed. Make note of strikes you get when making turns as they often indicate you should be moving slower (inside strike) or faster (outside strike). One other thing if it looks like you have something hitting your line a short burst of speed will often trigger a strike.