I have both - 03/04 Speedster GTS 166 and a 168 04/05 Silberpfeil. I don't think the GTS is the Speedster you want so I'll tell you about the Silberpfeil.
The board likes steeps and it is exactly as described "carving machine". There is no hold limit, carve as hard as you want - you never wash out and it's super fast going from one edge to the other. Riding it flat fast is not good, this board wants to carve - it don't like fast blue runs. You can go slow, you can go fast - as long as your hand is ready to grab snow you feel at home, it's only drawback: too much carve. Cuts easily through slush on groomed but sucks off-piste, it sinks.