Richard, I am probably wrong about field trial dogs.
My experience was with a very large Irish setter which was looking for food in alleys in our neighborhood. After leaving food for him for a few days, he finally would come into the yard.
We tried to find an owner- he had a collar with his name- but no answers to advs. or reports to the animal shelters.
The vet weighed him at 85 pounds (well above breed standards), treated him for worms and checked his health.
We had a little farm as a summer place and decided to keep him. He was somewhat of a wanderer, and we would sometimes trace him down several miles away.
He kept coyotes and other pests away, and would hunt out and destroy mouse nests around the graneries and barns. In the house however, he would be lying on the carpet, and his eyes would follow a mouse wandering across the floor, but he would not go after it. I guess he thought any animal in the house 'belonged'. He was a companion on any hikes, and would run at about 20 miles an hour, I clocked him once with the car.
Another vet, near the farm, said he had seem similar red setters in Ontario, where some people used them to chase deer, keep bear at bay, etc. That's what I meant by 'field', probably not in the breeders sense of the word. My experience is with terriers only.
One day he collapsed while running across the field and his heart had stopped. The same vet told me that about 10-12 years was the limit for them, but I have no personal knowledge of that.

A strange dog, always seeming to keep a little distance, never the 'loving' type, but we missed him when he died.