Meh this thing is old... and that processor is bad, well yeah, the open source nouveau drivers just arent that good for smooth 3D, but it could also be that the processor is simply too slow, how is your processor usage while emulating? if you can rule out the processor, try one of the 304 ones (doesn't matter which they are both the same) if that didn't work try the 173 one. If any of the proprietary nvidias work and it still stutters it's probably the processor that struggles