As an example I went back to the 7.5x500 Clock using 3.33 Divider giving 16667Mhxz DDr3
1N
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2N
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Looking at everest as the most consistent measure:-

So if your memory can run it it's worth about 1~2% extra mine needs to change at 1700Mhz at present on the Official F4
Bios. On the Asus P5E3 I was able to run 1T at 1800Mhz,