You could take a Connect3D X800GTO for some bucks less than the 6800GS, but seeing that its unlocking isn't as guaranteed as it used to be + the lack of SM3.0, I would personally pick the GS...
With the DFI and Sempron, you can easily hit 2.4GHz or more... 2.6GHz should even be possible... At that speed, it's roughly equal to an Athlon 64 3800+... Best value IMO...
BTW I took the ThermalTake PSU instead of the Fortron, because it has sleeved cables all the way, and it has (probably passive) PFC as well... (whereas the Fortron has none)
EDIT: D*mn, how silly... Only 18A on the single 12V rail... I expected it to have two... Take the Fortron then...