Michael „Wunnspeed“ Cleveland wrote a cool blog post about his 2013 GST ride. Read more here. I like his discription in his Flickr-album: 

„The Grenzsteintrophy race along the old East/West German border. You can find more info at overnighter.de. Honestly, I’d say it’s about 2X tougher than the Tour Divide in spite of the fact that the length is only 25% of the TDR route.“

BTW: You find all English information on the GST here (just scroll down to the bottom) 

PS: If you’re looking for costum made bikepacking bags in Europe, Michael is the person to talk to. Check out Spok Werks!