I worked on a OpenGL implementation for TPT in the past months and would like to have some feedback on its current performance. I focused on the particle drawing so menus are buggy and might even crash. Systems with weak graphics card (Notebooks, Netbooks, old PCs, etc.) will likely run slower with OGL.
Even if it doesn't increase performance (it will, if done properly ... with sdl you have all these nasty overheads that comes with all the function calls) it allows for more spectacular effects, and the possibility for more advanced scaling.