Welcome.
XMP sets the RAM to its rated speed, rather than the speed that the CPU or motherboard will allow. For example, an i5-2500K only supports 1333Mhz RAM, but enabling XMP will allow the RAM to run at 1600Mhz, 1866Mhz, etc.
It doesn't impact CPU clock speed, so you've nothing to worry about. Having RAM with heat spreaders is a good idea though.