Depends on the sticks, you just mention brand, many of the Hyper XI wouldn't touch, they have many at 1600 that take a voltage of 1.6 - 1.65 which is ridiculous for 1600, if that's what you are looking for - at 1600 and 1866 sticks look for 1.5 sets (the far majority of all 1600 sticks) - some of the Vengeance are the same - would need to know particular model you are looking at.
XMP stands for eXtreme Memory Profile, a standard developed by Intel, the sticks contain information in them that is passed to the BIOS for implementation that allows the DRAM to be optimally configured by the BIOS so the User doesn't have to do it manually