In the past week and a half, I've had three females all drop their first litters.
First is my varigated russian blue dumbo-who is important to what I want to work with
Second is my mink mismarked blaze-whose babies are only keep worthy if they have a wedge blaze
Third is a fawn with a perfect wedge blaze, but is kind of mean :/

The first two both dropped ten, but despite the fawn being older and larger than the other two, she only had six. I would just feed her off, but I really want to pass on her perfect wedge blaze. What should I do?
And also, when is a litter size too small to be worth it? When do you just retire/feed off the female and replace it with one that produces larger litters?