Great thread, lots of great info that I can learn from and I've been longlining many years.
Something that might help some, if using curly tails like Southern Pro or Kalins, trolling speed under .7 mph will not allow the tails to twist or have a good action. This will result in no bites. The curl or twist of the tail is what attracts the fish.
I have friends that will slow way down when fish are deeper rather than tying on heavier jigs or adding weight, and it never works. Some of them I simply cannot convince otherwise. Very seldom will you go under .8 or above 1.1 mph. I always start at .9 and adjust from there. And I always start with double 1/32 curly tail jigs. Double 1/32 simply outfish a single 1/16 for me in 95% of situations. I am very efficient at tying jigs, so I'm used to tying on 2 at the time after break offs.
If using Hal-Fly type jigs or minnows on other hand, you can troll slower.

I also only fish 4 rods, whether I'm driving or in the back as a partner. I used to do 6 or 8, but I have found that I can catch more with less. Less rods to watch and less tangles. Less tangles means more jigs in the water at any given time. I have a buddy that has a stick steer and fishes 8 on the front (4 off each side). He is constantly tangling his lines and rigging. He fishes 14,12,10,&8 footers off each side, so if he latches on to a big one or has multiple fish on, he ends up tangled with his other lines. He is constantly retying jigs, untangling lines, and trying to drive the boat. All the while, I'm in the back reeling fish in.