SWAG meaning----A good guess
"Scientific Wild Ass Guess"
Core to glass ratio is typically ignored by most bowyers. The industry standard is .040 on most bows ranging from 30-65 pounds in draw weight. But some bowyers prefer using .050 to have more flexibility on sanding the glass for weight reduction. I go up to .050 glass for 70-100# draw weights for durability. but realistically you could use .030 glass for anything below 40, but most guys don't do it for durability and stability reasons.
if you build two Identical 50 # bows using .040 and .050 glass. The .040 bow will be higher in performance just due to the mass weight decrease in the limbs.
The over all limb thickness is typically what determines the draw weight.
You will be surprised how close your actual limb thickness will be between .040 and .050 glass for the same draw weight bow. Probably be within .010 -.015 more for the .040..... but that core is much lighter in mass weight....
A lot of guys say cores don't matter, and in many cases its true to a certain extent. But.... the compression and tension values of the core wood can and will make a big difference in longevity and have an effect on performance as well.