with childreni, so i imagine macs are going to be similar, around the 300g mark fairly standard. a little less and they will probably still breed but you may only get a small clutch. I have heard of people getting a clutch with snakes around the 200g mark.
not sure if the weights of the breeders influence the hatchling size too much, but when it comes to feeding i've found the larger adults produced offspring that were much easier to get established.