I don't think the backing really matters as long as it's strong enough to hold the leadcore. It will not be seen and should not be the "breaking point". I've heard that mono releases better than dacron if you are using planer boards...if you aren't using boards then it just doesn't matter. I'm going to try dragging less colors and put out more backing to get deeper this year...4, 5 and 6 colors on my rods. I moved from 30ft of mono between leader and leadcore to 100 ft this year and really saw no difference in catch rates. The nicest thing was being able to fight fish one the mono for longer so it felt more like using DR rods. It was a lot more work checking lines.
i like a long leader for playing the fish, it also gives me the option to run that long leader on the downriggers. with the long leader, flies work better for me, spoons not so much, and i can use the fly rods on the downriggers