I like reading Dr. Ashby's tests, but seems like lots of folks are reading his reports and deciding they now need grizzly heads or they have to single bevel their existing heads to shoot the deer they've been shooting for years without any problems.
Grizzly, Zwickey, Eclipse, Stos etc ... are all going to make the same basic cut, and they're all tough.
I also find it very interesting that the majority of tales/pics we see of folks who go to Africa and Australia to shoot big stuff ... aren't using grizzly heads. They're using the same zwickeys, magnus', eclipse's, stos', woodsman's etc... that have worked all along.