I've got a metcalf, your estimate sounds about right. I've had it loaded to 65lbs plus 7 lbs of rifle. Its comfortable at that weight, doesnt not feel like its pulling away or down at all, higher load lifters are WAAYYY better than the crew cab was. I\ll be taking this pack on 12 day sheep trip up the muskwa come August. The metcalf is a huge improvement over the crew cab in my mind, I took the lid of and emptied the pack out save water/snacks/spotter, it felt non existent and had zero movement when the compression straps were cinched down.
I would love to see MR come out with a spottig scope pocket similar to what the stone glacier pack has.