PM if you want to discuss this. It's interesting and I just went through this. First dog was very small, aggressive to the whole family, bit my daughter and had to go. She is a great hunting dog and because of that fact, she was adopted by the trainer I was working with. Lucky for her and me as otherwise not sure what would've happened to her. She is now 34lbs @ 10 months.....so very small dog. She was out of FOX GLOVE kennel in Vancouver.....DO NOT GET A DOG FROM THEM... I'm happy to explain the 10 reasons why.
Fast forward..
Got another GSP pup, 3 months ago, from a guy who bred his dog and just had one litter. We were very selective before choosing him....Interestingly his female(and the pups) are large dogs. My pup is now about 50lbs @ 6 months old. Vet says she will be 60-70 lbs. She has a great disposition, is hunting well and training is going well.(has 5 birds shot over her so far) Anyhow, after hunting with and owning several shorthairs over the years, I believe the larger dogs tend to have a better disposition, while still being good hunters. Yes, small dogs might be more nimble hunters, but for a dog needs to fit in with the family. Yes, there are many variables concerning the parents and lines, etc. but assuming they parents are good hunters and i could choose between a large and small GSP...I would pick one the larger one.