We had two growing up. One I remember (her name was Britta) - I grew up with her and the other girl, Cleo, I do not because I was very, very young when she died.
From my limited experience, they were great dogs. Very active and outgoing of course and very happy to spend a lot of time playing with very active children. Our two did have a protective streak IMO, but really I'm not sure if it was anymore obvious than in any other dog we've had. Gracie doesn't have a protective bone in her body. Humans = friends. Period. And Abby is 'weird with strangers' so I don't have much to compare with.
Britta would always bark and carry on if someone entered the yard, but once we had let them in and she knew it was ok, she'd settle straight back down. She was fine with visitors or strangers down the street, but she'd have quite some stuff to say about those that just appeared in our yard.
One night she was barking quite persistently, which was strange because she wasn't much of a barker. My father ended up yelling at her to shut up. The next morning dad discovered our car had been siphoned. He felt pretty silly about it and took Britta rather seriously after that. Lol, not one of his best moments for sure.
But that description could be of any dog really. She once bailed up my brother's friend (young adults at the time - there is quite an age gap between us kids) in the middle of the night because he had come into the backyard and through the downstairs of the house instead of going through the front yard as per the instructions. She didn't hurt him at all, but gave him a big fright and we had to diffuse the situation.
Also, when she was much older and going blind she once half bailed up my dad who had come out of nowhere really and the rest of us were downstairs with her. I personally think she just got a big fright on this occasion and was slightly confused. She immediately looked shocked at herself when she found out it was dad and showered him with kisses instead.
I have heard similar stories about Cleo.
So, although I wouldn't know if the breed is protective as a whole, I know the two we had did have that characteristic. But at the same time I wouldn't describe them as 'weird with strangers'.
Edit - these two dogs were very sound in temperament I think. I have since met some GSPs out and about and some of them seem quite highly strung... I can't tell whether it's just their temp or if it has something to do with perhaps lack of exercise/too much energy.