<< in the mean time - the closer the fsb/ddr ratio is the better off you are in terms of latency performance.
the wider the ratio, the worse it gets >>
I'm not sure where you're getting that. See, the fsb/ddr ratio is simply the BIOS' way of configuring the DDR/fsb clocks, while all that really matters is the frequency, and there are only 2 configurations where the fsb and the Memory clock are synchorous for the P4. The first is a 400MHz fsb with PC1600 DDR, the other one is a 533fsb with PC2100 DDR. See, the P4's fsb is QDR so the real frequency for the fsb is 100 (400fsb) and 133 (533fsb), and for DDR, the real frequencies are 100 (PC1600), 133 (PC2100), 166 (PC2700), and 200 (PC3200). And if anything, the latency for DDR400 is going to be worse than PC2700 because for DDR, the latency increases as frequency does. That's why in benchmarks you see minimal improvement from PC2100 to PC2700, and all why you see next to no real world improvement from PC2700 to DDR400. Just my 2c