I've definately heard and read in quite a few places that the smaller the female the less chance of getting a good quantity of viable eggs. In fact, I know someone whos 2900 gram female laid a clutch of 13and 12 of those hatches
I also know someone who has bred 2 different females under 1600 grams and both laid 4 eggs each and one of the eggs was a slug. So I don't know I assume each snake is different (just like each animal or human is different) but as a rule I would think breeding less than 1500 grams is not the greatest idea....as you said especially if they aren't great eaters.