I've had 2 what I would have called "runts" as a breeder. Both were born about half the size of the other puppies and stuggled to make it in the beginning. One grew up to be an 85 lbs male, beautiful! Not a washout, he loves to hunt & is a great family dog. He learned quickly with his novice owner trainer. The other one, a female was always different. She was fast as the wind and love to play but seemed to suffer from the "PeterPan" syndrome - she never grew up - she is the perpetual puppy. She was given to a home as a pet and I have not heard from her owners in a while. They love her and think her quirkiness is cute.
We bought the smallest puppy of a litter once. At 7 weeks old he weighed 6 lbs. At maturity he was 50 lbs. and the best marking dog we have had. He was definately not a washout. Lotto is not 10.5 years old and still very puppy-ish....but when the marks stary flying he is all business and just needs you to be is caddy. He got his HRCH-MH titles and passed the Master National, doing more that we ever dreamed we'd be able to do with our dogs. At the last vet visit this fall, our vet was doing her hands on physical can asked for the 2nd time...how old did you say this dog is? we said that he was 10 last July...and she just shook her head and said he certainly don't feel like an old dog. His muscles are still very firm and he has almost no gray.