I found a piece of gold: http://olofson.net/download/smoothscroll-1.1.tar.gz

It has two modes, OpenGL and SDL. In SDL-mode it doesn't vsync for me, lots of image tearing is visible on the display. The SDL-mode uses about 65% of my cpu. In OpenGL-mode it is vsynced, eveything scrolls smoothly, and only 3,5% cpu is used.