There is an interesting website which allows us to simulate the triode loadline, or in other words: Triode Loadline Calculator. The link is here. You can easily drag-and-drop the curver inside the chart to simulate the impact on other parameters.
So far the tube selection is a bit limited to popular tube like 2A3, 300B, 6SN7, and several ECC tubes. I think the owner could easily expand this software to cover more tubes.