I'm a software engineer so I do happen to know a lot about "threaded" applications and how they can effectively be used on multiple CPUs.
Do you have a link to these claimed "performance gains"? I'd be surprised if they have anything to do with "multi-core support" -- they may perform some other tricks so that the graphics processor can process more tasks simultaneously to get the job done faster but those same tricks would be available to single or dual core processors. They may have provided "support" so that if they receive two or more threads at the same time which they can martial the threads to process them without necessarily using FIFO (that would be DX9 function dependant -- meaning you can't render pixel shader until you've rendered the polygon and added texture surfaces). So some task may translate well others no benefit -- however, it is a good direction to go in and I'm glad nVidia are thinking ahead.
But sure, bring on any X2 processor against FX57 and use current crop of games and lets see which processor does better. From all the Test results I've seen for real world frame rate improvements in games the FX57 is still top of the food chain.
But regardless of the "supported" features, it will be a long time before we see games that truely benefit and use more than one processor (afterall, multi-processor systems have already been around a LONG LONG time and that didn't motivate game developers to start coding for multiple threads assigned to specific CPUs). But even optimistic use of multiple processors will rarely produce anything more than a 25-33% performance increase. Classic example of this is current 4 and 8 CPU servers that can't process a task any faster, but can handle many more tasks at the same time so that they don't slow down as much when loaded up with threads -- at some point tasks are waiting on each other to finish so the next logical dependancy can start -- so having dual cores will never ever give you 2X performance increase even with the most efficient game designed for multiple processors.
Don't fall for the X2 hype -- we can hope it will move game developers forward towards CPU specific threading (not just general OS/driver threading) but that is just a "hope" -- money & time will ultimately either leave it in or out of the game/software design.
Rob.