Hey Skifish,
I think Cannon downriggers are rated up to 10 pounds and Scotty's are rated up to 15 pounds. The heavier the weight the more vertical the wire and the closer the readout on the rigger is to the correct depth.
I have Cannon Mag 20 DT's and I use an 8 pound coated ball w/ a fin to stabilize it.
Hope this helps.
randy