What changes line speed
Layers of line
At a constant drum RPM, line speed increases with each added layer of line on the drum. Line on the first layer moves at the slowest speed; each successive layer is faster because the diameter the line wraps around keeps growing.
Drum core diameter
For a given input speed and drum torque, a larger drum core diameter raises line speed — and lowers line pull by the same proportion.
Rated vs. working layer. Columbia ratings are first-layer line pull and line speed. When you size a unit, check the speed and pull on the layer the drum will actually be working on.
Speed and pull trade off against horsepower: see Horsepower.