I finally managed to solve the San Andreas running too fast-problem by installing the 190.62 NVIDIA driver. But the solution came with a new problem. The screen now goes black or turns into thousands of horizontal lines frequently while playing. The game keeps running with sound and everything but the picture is gone, so this is obviously a video-problem. To restore the picture I just have to alt+tab and maximize it again but this happens really often so I cant live with it.