But the differences are so small that you will not even notice. The speed of the QPI bus is ridiculously fast. At the default 133 BCLK it's twice as fast as a 1600Mhz FSB. In adition, the internal memory controller is so much more efficient at communicating with RAM than the northbridge...
I've been using a Mamba since May last year, and love it. Back when it first came out there was a click jitter issue due to the lack of teflon ring around the sensor, but that was fixed. Also the z-axis tracking issue when lifting up the mouse is greatly exaggerated. I didn't even know it...