Personally the only way I have caught walleye in sub 40 degree water is with smaller shallow stick baits trolled 1mph or less. With a 3/8 oz rubbercore weight attached a rods length ahead of the baits, you can get them deeper and keep debris from fouling your lure. Also with running boards you can use shorter dropbacks and get better hooksets. 25-65 back is a good start, if you want to probe deeper than 15' try deep divers or shallow baits down on a rigger. Most of the fish will be suspended so keep a couple high usually on the outside board, with the deeper ones in the middle. Thunderstick jrs, smaller Husky jerks will have the slow roll actions for trolling at these speeds. Once water is above 45 you can switch to larger raps, shads, and tots which do well in mac in the summer. Troll the breaklines and open water. Look for cleaner water areas, but the mud will warm up quicker.
We almost went to Holland, but heard it was real muddy, and tried for some of the big pike I hear about on Pigeon, but have never seen one.
Still beats working.
Once the season closes and the fish start dropping back they will be going good off the pierheads in Lake Mi during April (where no closed season) at night. Maybe we can go sometime when that action starts.