I purchased some Corsair Vengeance LPX 3000MHz (4x16GB) to upgrade my 5820 tower.  According to the memory configuration the memory should be accessed at 2667MHz.  But when I boot the server and check the BIOS, the frequency is set to 2133MHz.  I don't see any settings related to XMP in the BIOS.  I contacted Dell and was told that the memory speed was "auto detected" and there was no way to set it.

Should I have purchased the LPX 2667MHz memory instead?  I grabbed the 3000 because it only cost 1 dollar more.  Alternatively, are there recommended memory modules known to work at 2667 with the 5820?  The memory from Dell is extremely expensive.