Dell :: Raw Compute Performance Difference Between M4400 And M6400

The M4400 supports dual-channel DDR2-800 memory.
The M6400 supports dual-channel DDR3-1066 memory.
Both systems have a FSB that operates at 1066 MHz.

I'm trying to understand if the different memory technologies ultimately make a difference for computational (i.e. math on large data sets) performance in these particular machines.

Consider an M4400 and M6400 with identical CPUs and amounts of DDR-2 and DDR-3 memory, respectively. And suppose that all relevant memory latencies are identical. For the sake of this question, I don't care about power consumption and heat (which is obviously a benefit of DDR3).

Question:
Since both machines support dual-channel memory operation, the maximum effective bandwidth of the memory bus is doubled. So the dual-channel DDR2-800 can achieve 12.8 GB/sec transfer rate, while the dual-channel DDR3-1066 can achieve 17 GB/sec transfer rate. In either case, these rates are higher than the 8.5 GB/sec rate that the FSB can achieve, so it seems that performance in both machines is limited by the speed of the FSB (1066 MHz). Is that correct?

For more info on matched FSB and memory ratings under Core 2, see:
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