Just be sure that both parents have good hips and the parentage is cleared for dm. I see where not all the adults have their hip rating listed. No personal experience though. My Sting is oversize - 30 inches tall 130 lbs but from not specifically bred to be that big -he was just twice as big as the others in the litter. He has a good drive and doesn't fit the usual temperament description of the oversize ones. You could ask the breeder for some references and also visit them and meet their dogs before deciding on a pup.
Sting Chance von Gaard AKC GSD 2/8/2006