Ballistix no one ran xmp on x58 because you overclocked with bclk, xmp is necessary to get higher performance beyond jedec standards and i would argue that most people are happy to just turn on xmp in bios and be done than take days to run all the permutations with frequency and timings to squeeze all the performance out off a ram kit
That was for the CPU, you could still pick what frequency to run the ram at.
XMP is not necessary at all when you can get the exact same result and often even better from manually overclocking the ram, at best its just a shortcut.
If you by a kit that says 4000 MHz CL18, then its easy as selecting 4000 Mhz and inputting the timings and voltage (which still isn't guaranteed to work on your mobo / CPU). 'Pre overclocked' ram also carries a massive price premium that is rarely worth paying for over manual overclocking, and the performance gains are usually minuscule anyway.
As an example, 3200 Samsung B Die is always a better choice than 3600+ anything else because you can simply manually overclock it and get far better results.