Ozy,
An interesting trend has begun to show up in my testing. I can't say why but, it appears that almost any single bevel head will hold it's edge far longer than a double bevel. I posted a while back about Grizzlies and the tough steel when I couldn't dull a sharpened Grizzly by cutting into a solid aluminum block repeatedly. Since then I've tried the same thing with Tuskers, Abowyers, and Steelforce single bevels with similar results. Like I said, can't give you the scientific reason for this but it's a very interesting phenomenon.
Ron