I'm also confused about this!
I'm 5'8" with bony wrists and elbows but my bones are large and even at this weight I look bony all over my body. I have very broad shoulders, large hands, large feet. I begin to look very ill and very gaunt around 140 lbs or so.
I believe I have a large frame/large bones because of my wide shoulders, ribcage, and how my collar bones, ribs, wrists, and elbows already protrude a LOT at 180ish lbs.
Anyway, you could always pick medium-high end 'normal' weight range for your BMI and see how you feel once you get there. If you look good and are happy, stay there. If you want to lose a bit more, go for more! I picked a number closer to the high end for 5'8" and I'll see if I'd like to stay there once I'm 160 or just work on toning or go for another 5-10 lbs. I still have a way to go so no worries yet.
