Thanx a lot Kwag, this is really a good news.

Now, I've got the feeling that the high bitrate peaks appear, above al, when there's a sudden change from a low bitrate to a high bitrate situation in the film.
There I can see the peak, and then mencoder raises quantizers and slow down. Is this the situation you could "generate" in your test, or was that continous high bitrate demanding?. I can't imagine a way to reproduce the situation I describe.

Anyway, it's good to know that mencoder can limit to maxrate in this difficult situation you created.