Patch to get the above result is available on request, likely I'll open a new branch in SuperTux SVN in the next days.
Some other issues the game currently has:
- tearing is currently rather obvious and annoying
- the game doesn't have fixed size steps, so if the computer gets busy with other stuff it makes large jumps, often deadly for Tux
- calling the sugar frame and similar adjustments sometimes doesn't work properly
- alpha-blending, it is likely worth it to get rid of any of that to get faster fps