XMP is DDR3 and DDR4 timing. This was never an option for DDR2. You are asking about a feature that does not exist on your system. There is no OVERCLOCKING on any Precision or Optiplex model. Extreme Memory Profile (XMP) is a specification serving as an extension to the standard JEDEC SPD specifications developed by Intel. XMP is intended to make overclocking easier and more accessible.
I have a Dell T5400 with Dual X5460's, 12 GB of DDR2 FB-DIMM RAM, and a GTX 960, are there any ways to have an XMP enabled BIOS?
Dell T5400 RAM