Good discussion going here. Thought I would throw in a couple of comments.
First, LoweSTS175, there really isn't a wrong way to tie a worm harness, slow death or regular. Some work a little better than others, but all catch fish. I tie them bead, mack's smile blade, bead, float, smallest swivel, slow death hook.
Second, I troll at an ever changing speed - 1.8 to 2.6. When I get hit, I narrow the range to something on both sides of the hit speed, but I still experiment. I remember one trip to Broken Bow in Oklahoma where people could have water skied at the speed the fish wanted.
Third, my experience tells me speed does not affect depth until the speed causes the bait to kick out and lose traction.
BTW, I posted an article on trolling for walleye on Phil's forum some years ago. You might want to take a peek. "Trolling for White River Walleye"