Okay, there was a thread recently that got me started on this. Somebody asked how much you level-up in % for each trophy you get, and how that related to what level you're at. WhiteWolfDK answered the question, so hopefully his original thread makes it to the new site and I can link to it here. All I've done below is expand upon work that WhiteWolf did. Enjoy!
Data with percentages:
Same data, but in graphical form:
Zooming in a little, taking out outliers:
Zooming in even more: