You're asking a loaded question there,
@firmwood. Let me tell you a big secret that most foresters and log buyers don't know, but all fallers do. Brace yourself, here comes.
A graded standing log that is still part of a tree and a scaled log on the ground are not the same thing.
This is hugely important because we prepare and sell our timber as though they were the same, and then the sale administrators have to run interference between us and the buyers over the difference. The fact is that when I'm cruising standing timber, I can only tell you what I can see. I can tell you how tall, what diameter, what defect is visible, etc. I can't say anything about hidden defect, or damage during falling, or cull due to forks, or whatever else ends up being a deduction between landing and mill. Utilization is all about the skill and expertise of the faller and the rigging/landing crew.
In the end it doens't matter a lot how you grade your standing timber, so long as you pick a method and master it, and use it consistently. As far as volume per area, you're gonna want to think about variable probability sampling, which is an education in itself. If you're only talking about a hundred or so trees in a limited area, you'll probably be best off either tallying by diameter or by simply measuring all of your take trees individually. Your volumes are going to be all over the place because of the crown shape. Butt logs are easy enough to model for but topwood is a whole different ball of wax.