Just plugged 8GB of G.Skill 2133 mhz ram into my desktop. The memory clock speed stayed at 1333 mhz when I did so which led to some fiddling with bios settings.
I have a Gigabyte P55-USB3 motherboard with an i5 2.8 Ghz processor and plugged in 2 x 4GB modules of the F3-17000CL11D Ripjaws ram from G.Skill (in a nice red color to boot). Motherboard manual is here, http://www.gigabyte.com/products/product-page.aspx?pid=3440#manual
Once in the bios config in the ‘MB Intelligent Tweaker’, the ‘Advanced Memory Settings’ seemed to have what I needed, ‘Extreme Memory Profiles’ for different speeds. Profile 2 put the speed at 2130 mhz and all the advanced timing settings matched the memory specs (11-11-11-30 2N). Unfortunately, it wouldn’t boot. Switching between the different profiles (disabled, profile 1, profile 2) and ‘Performance Enhance’ modes (standard, turbo, extreme) didn’t help much, the only way I could boot was at 1600 Mhz in the disabled profile with extreme performance enhance.
Fortunately I hit on a nice overclocking guide, http://www.overclockers.com/3-step-guide-overclock-core-i3-i5-i7/
Leaving the memory settings at the default values, I went into the ‘Advanced Frequency Settings’ section and changed the Base Clock BCLK to 200Mz with the CPU Clock Ratio at 16x. This gave me an overclocked CPU speed of 3.2 Ghz (seemed reasonable and a nice bonus) and put the Memory Frequency at 2000 MHZ (good enough).
After a few hours of serious programming work, the system has been completely stable and seems a bit faster. Hope that helps.