I finally got my hands on a #66 today, a second from the ironwood run, due to a slight split in the timber.
Overall, I like this knife, but I think its slightly chunkier and less graceful than the smaller Schrade and Primble stockmans I am used to carrying in my pocket to work (I work in an office job). There is a slightly unnecessary heft to the knife, which pushes it a little bit outside the perfect asthetic.
I think a reason for this is the additional liner on one side, which seems to be there to give greater clearance to the spey blade in its closed position. This seems to reduce the crink of the sheepsfoot blade, it runs straighter than in my other stockmans. I thought this extra liner on the secondary blade may have the effect of reducing the thickness of the secondary backspring, but it seems to be the case that a thinner secondary backspring is a common feature for knives with a smaller secondary blade.
In any event, the second liner on one side helps to make the #66 noticeably thicker than comparable models of similar length.
Otherwise, this is a really nice knife and since it was a second, I may end up using this one.