We rescued a shepherd/rottie mix from the SPCA he was skinny and unhealthy and he was 80lbs.
Now he is healthy and very active, he is currently 140lbs solid, so I guess that's a guide to the size you can expect.
He is 4 years old and is one of the best dogs I ever had.
I have a rotweiler/ german shepherd and he is 7.5 months at 75 pounds. The vet says he thinks he will be around 85-90 pounds. He is lean like a shepherd.