Well done Steve.
Using the best of lots of really short exposures is the only real way to get the best resolution on such a bright deep sky object, rather like planetary imaging.
Eddie Trimarchi, being typically way ahead of everyone else did an excellent example of the Keyhole area (one of the best ever IMO!) some year ago now with his lill'ol C11 using this technique, he used very long focal length too:
http://astroshed.com/st10pics/eta.jpg
Pretty amazing huh? Look at the homunculus (sp?) arount Eta
Mike