Forgot to mention: I will take six (6) of the 11 X 4.5 and six (6) of the 12.5 X 5.5.
The first pack of six that I bought cost something like $12 plus tax. For about $2 each, I should have bought many more at that price.
Regarding stiffness as compared to other props: Of course, it is not as stiff as a carbon fiber prop. I would say that it is about equal in stiffness, maybe a bit less, to a similarly sized wood prop, such as BY & O.