I know that a lot of people have asked this before, and I understand that just like with people there are all kinds of variatiosn.
Still... with all the breeders out there I'm surprised we don't have the equivelent of that percentile height/weight chart you always used to see in the doctor's office as a kid.
Something like 90% of BP's will be at least 18 inches at 3 months and 75% will be at least 24. Or something like that.
There will always be outliers, but we could at least get a feel for what average is.