Trolling - Leadcore and Copper
If you want to get down to 50ft or slightly deeper, the Offshore Tackle Magnum Tadpole seems like it would do the job. On the dive charts on Offhore Tackle website it shows that with 20# test mono it will go to 48ft with 150ft of line. I would sure think with 10-12# test it would go deeper than that.
18 LB Leadcore will sink about 5' per color of line out. If you are running say a 10' mono leader with a shad reap or spinnner in you case, and have 4 colors of leadcore out, your bait will sink about 20' at 1-3 MPH. Keepo in mind that with leadcore the slower you go the more is sinks, that faster you go, the less it sinks. I typically run leadcore at 1.5+ MPH.
Im not sure about sink rates at those speeds but I would skip the lead and coppers altogether and use inline weights. a 1oz inline will go down 1 foot for every 2 feet let out. so 40 out is 20 down. very predictable and easy to use.