Grake, apparently a good indicator of the size of your bub is how big you were born. This is what my Ob told me. One of the first questions he asked me was how big I was born. So we were told from very early on that we would be have a largish bub. My sister also had big bubs.
This is an interesting theory.

I was only just on 6lbs when I was born and have had 8lb 7oz and a 9lb 7oz babies. My DH is a big guy though and when my current ob was going on about me having another 4kg+ baby I asked her about the hereditary thing and that maybe they were just taking after their Dad's side of the family. The ob said that wasn't very likely and that in fact it was my DD who might have issues when she gets pregnant with her own babies - that they will be really big.

But then my own experience blows this theory out of the water...by rights I should only be having little babies, with little heads, instead of the strapping big babies I am actually producing!