7900'S were just a die shrinked 7800, abliet lower price due to higher yields per wafer and the subsequent reduction in heat while running allowing for a tad higher base clack speed.
When Vista is released this fall, the "pro" version will utilize dual core. Applications such as Photoshop and 3dsmax already will take advantage of dual core/dual cpu. I typically will have Solidworks(CAD), Photoshop, Max and Ued open all at the same time, any of which can bring a rig to it's knees on their own.
Just saw this baby, looks sweet, only I won't have a rear exhaust fan if I get the PC3077
Freezone CPU cooler