How similar are these two shoes? I have narrow feet and have used the Classic with success, but our team as access to Nike shoes. I'm actually mostly neutral, but might benefit from a little stability as I've noticed that my right leg in my Haywards seems to pronate very slightly. I don't think a very stable shoe would work well.
If you pronate slightly, stay away from the Structure. That shoe has gotten beefier and beefier over the years. I believe that they are re-releasing the Span, so that could be a good option if you can get it. Other than that, maybe just try the Pegasus if you want the free shoes. However, I don't think the Pegasus is that great anymore either...