The guidelines I follow for calculating lead core sink rate:
5’ per color at 2mph
7’ per color at 1.5 mph
10’ per color at 1.0 mph
add to that 1/2 of the dive curve depth for the lure you are using for the amount/type of line in the water.
As Eyeman pointed out when you turn the inside lines will slow and sink faster and the outside lines will speed up and rise. This speed/depth change is often when You will get bit as it triggers a follower to strike so running shallow “S” curves is an often used tactic, just be aware a sharp turn will have the inside lines sinking rapidly and can lead to problems. ‘Smooth” turning makes life simpler and more trouble free. Just as speeding up will make the bait rise, if I mark good fish below the level I am trolling I can s l o w down and let my lines take the lures down to that range as I pass(within reason) and sometime pick those fish off. If is a very effective system, but as MG pointed out not very sporting with smaller fish. Hook up with a large hybrid, striper, or big blue cat and that lead line is unnoticeable.
Mike