In the bay we use 18 to 30 oz jigs to 3 way rig. I would try a 6 to 8 oz to get the lure down to the depth you want with whatever dropper you want on the back 3way. ou can try any sizes you want to get to the desired depth.
Good luck
spooplugs are actually divin plugs, not dependant on weight, but design, to get them down. an, yes, many use the sutton and similar type spoons on 3-way with a bucktail jig. use it myself on leadcore so jig weight would not need to be so heavy to reach desired depth. hope this helps ya catch more fish!
there are 7 different sizes of spoonplugs. the #500 runs 2-4ft deep on 12 no-bo line, bout the same dia. as 20 mono. the 400 runs 4-6ft, the 250 runs 6-9ft, the 200 runs 9 -12ft, the 100 runs 12-15ft, the 700 15-20ft, the 800 20-25ft. ya can double that depth with a weighted line (wire or leadcore). so ya can fish down to 50ft. have caught fish deeper than that in fresh water, but had to go to live bait to be successful at such depths. hope this clears things up!...FD