just one more

So, what would be the deepest you can would go with this set up??

New to running dipseys this year and have a question. What is the max that a dipsey will dive before it plains off? I'm running 2 10' rods one on ea. side with 30# wire and #1 dipseys set @ 2. I run spinnies/fly combos on them. My speed ranges from 2 to 3 mph. I know I get about 30' down for every 100' back. My question is what is the point where the depth deminishes? Someone said about 300' back will get you 90' down and that is about it. Does that sound right? Thanks for you imput!