I use X-line... it's a flurocarb mainline and it sinks like a brick... I use it for fishing slack lines running rigs in the winter because it doesn't spook the fish
In the summer I use it as a leader because it a flurocarbon it's almost invisable and it sink so you cant see it on the water surface... if you couple this with a floating mainline (daiwa sensor lubed with vasaline) then your set for a good session!
I managed 2 pasties of 9lbish a 15.2lb almost linear and a 20.2lb mirror in a few hours on my local HAPPY DAYS!