5.5 per side is fine if the knife is hard enough, but the range you are specifying isn't there. I would take the 5.5 if it were at 65 or 66 HRC, otherwise, I'd put a small microbevel in it.

Here's what happens when you get D2 too thin. This is a Queen 4180 that I took down to about 12 deg. This damage was caused by cutting fuzz sticks in pine - not a terribly demanding task. Up until this point, I thought this was the be-all end-all combination, as it would slice cardboard all day.

On the bright side, it's thin enough that I removed 95% of the damage with a small micro bevel on a DMT blue in about 3 minutes. It doesn't cut quite as well with the microbevel, but is still miles ahead of lots of other knives in my collection. And it resists damage quite well now.

I chalked it up to learning the limits of D2...

http://i137.photobucket.com/albums/q203/sodak_photos/queen_4180.jpg