.440 is what I used and it will end up 45# I'm almost there now.
Mine was just a guess going off my records from previous longbows built. JF
Changing limb width is linear. IOW, a limb 2" wide and 50# would be reduced to 25# if the limb were reduced to 1".
As regards limb thickness, the changes in thickness effect draw weight with a factor of eight.
I have two stack calculators and they both function based on that math. They aren't perfect but they are very very close.
For the type of bows that you mostly build, as do I, the Bingham chart is very close but you have to remember that it's based on the width of the Bingham design. But, it's very easy to use the linear aspect of the width formula to calculate weight.