Carsten,
Here is a patch for a new 'est+' summary type, including corresponding changes for xemacs and the manual. I've done basic testing on the GNU emacs version, but not the xemacs code.  

I'm not sure the change to the manual provides the right amount of information
in the right place; I'd be happy to re-write to make it find in
better. Similarly, the name of the summary type is entirely up to you.

I didn't know whether to send this directly to you, or to the list; if it should go to the list I'd be happy to send it there directly.

Thanks for the chance to contribute,
Mike