Getting 2 different sets to work together

[Unrivaledx21]

I realise that this is not recommended. I already have these sets though so what I am wondering is the best way to make them compatible in xmp. Both sets are the exact same model of RAM with one set being purchased roughly 2 years later. I've managed to get the system stable with XMP off, but when using XMP the system gets a BSOD randomly during usage. I realise that XMP would be specific to one set, but is there any specific settings / timings that I can adjust to assure stability with XMP enabled?

 

[Unrivaledx21]

Thanks a lot for your response. I've managed to have success and a noticeable improvement by turning XMP on and increasing the tRFC to 314 and the dram voltage to 1.6. The ram itself is specified 1866mhz 9-10-9 28 at 1.5v. I did try to change the voltage though to 1.55v and had a BSOD within 10 minutes, so have increased it back to 1.6v. I may even attempt to push this ram to 2133mhz at some point, but not sure whether it is worth it if it requires increasing the timings.