I can get close by test floating a jerkbait in 60 degree water in my shop. My water gets colder than that, but I use is as a starting point. On the water, I can adjust the float/sink by using either monofilament, which floats, or fluorocarbon, which sinks. Close counts. As long as the bait moves very slowly, either up or down, at rest it will work. Having the patience to test in the shop is the key, because I start with a known quantity that I can adjust on the water.