Nope, they are the same in my experience with rump whites. Although as a marked variety the rumpwhites may be generally producing slightly smaller babies anyway. I have seen a few litters of reds as well and I'm sure they were of average size.
Id never really thought about it but it should in theory give the pinkies a bit of a boost although it doesnt seem to. Maybe the sytem of growing the babies in the uterus is less competative than the after birth fight for milk.
Hmm...thanks you all. That's fascinating. What made me wonder is that I currently have 2 litters from sisters bred to their father in a very inbred line. One sister had 5 very large babies and one had 14 small babies. I figured in varieties that routinely have smaller litters the babies would be bigger, but I guess not.