In the market place, there is a guy selling a 72" with an Evolution 26 on it. He had a video of his plane. The performance looks pretty good!
The video is posted here:
http://media.putfile.com/Yak-54-78
Not sure about how much his plane weighs though but hopefully this will give some of you an idea of how this size engine performs on the 72" (the 73" should be comparable)