but is it possible for some to explain the micro stuttering so I can understand what it is?
Say you're running a single GPU, and you're running a game at 30FPS, the frames will all come at regular intevals.
Now, if you're running a multi-GPU card or configuration, the although the frame rate may be higher, the frames will not be at regular intevals. Example: one frame comes 10ms after the previous one, the next comes 40ms after, the next 30ms, and so on...
What all that means is that the lowest playable frame rate with a multi-GPU configuration will be greatly increased in comparison to a single-GPU.
Crysis may be playable at 30FPS with the 4870, whereas it may not be playable with the 9800GX2 at the same frame rate, simply because the frames are not at regular intervals.