I had to bring my girl home very early. She was nearly 5wks, I didn't have a choice though it was take her or not, and she only had two siblings. I agree with Pax8 it's great for them to stay longer and learn things from their siblings & such. That time frame is also when a lot of pups begin their journeys to their new homes. It's just a matter of your preference here I think. You won't end up in a mess like I did, and if few to any of his siblings are sticking around that long I'd say bring him home! Congrats on the new addition, and it's great you've got so much time to devote in the beginning that really makes a difference in rearing a pup especially GSD's I've found. Post pics for us when you get him!!
Sable GSD 3/2014
Stewart Australian Shepherd 5/2006
Babe Daschund 2/2006