|Cpu state||Speed (gb/s)
|Core 2 Duo|
|Core 0||Core 1||Core 0||Core 1|
|Core 2 Quad|
|Core 0||Core 1||Core 2||Core 3||Core 0||Core 1||Core 2||Core 3|
Have you verified that something else running on the system is not affecting the test results?
The O/S might favor one of the cores for some of the services. Favoring one of the cores would knock down the performance on it's partner coreas well. Something as innocous as refreshing the video adapter could cause similar anomalies as well. Try running your test while the system is in a full screen console window (i.e. VGA text mode using Alt-Enter). And make sure the test is not blasting out results data to the screen.
From a cursory look at your test results it would appear that the memory band width for both systems is ~6.0 GB/s.
The fact that you see 5.5 GB/s on the Core 2 Duo indicates that there is a 0.5 GB/s "drain" on the system. I use drain here to indicate whatever it is that is interfereing with memory access.
On the Quad, it appears that this drain affects cores 0/2. As you can see from your charts, when more than one core is active that no one core attains 5.5 GB/s or even 4.5 GB/s as this is due to contending cores waiting for their turn at the memory controller. The drain on 0/2 is likely causing a statical loss of being first at the memory controller during an otherwise tie-ing situation. i.e. cores 0/2 statistacally loose out on average what would otherwise be a tie-ing race condition.
Someone at Intel probably has written a white paper on this.