Thanks for letting us know about your experiment. I always like to hear about the results of experiments like this. One thing I do notice, however, is that the CP of your machamps is significantly lower than the other pokemon on your list. Therefore, they would have gained you the most prestige if you used them for prestiging purposes. For attacking they wouldn't have been as good for you, but are they also lower level than the others?
What are the levels and IVs of the pokemon used?