G. Skill Ripjaws X DDR3-1866, running at 1333Mhz?

The default setting for DDR3 is 1333 MHz. This means that unless you manually select a different frequency, you'll always run at 1333 MHz. You are correct in your assessment that "O.C." stands for "overclocked", which does mean that you have to overclock your RAM to attain the desired frequency above the 1333 MHz rating. I believe the A2X4 645 can support the 1600, but honestly, the difference is negligible at best. That is, unless you're comparing benchmark results, you won't notice the difference between the frequencies.

Perhaps. Other points to consider when evaluating RAM are the latency, or timing and voltage.

The latency is shown as X-X-X-X. The gist of these numbers is that they indicate the amount of clock cycles data transfers at. As you might of guessed, lower latency is better. The voltage specification is the recommended amount of voltage to operate the RAM at optimal settings. In this case, lower is also better. Now, let's put this into perspective.

Let's say your G.Skills have the following specs: 9-9-9-27 1.6V @ 1866 and your value RAM has these specs: 8-7-7-24 1.7V @ 1333. This means that the manufacturers have done enough tests to identify that their respective RAM operates best at the specified settings. You can go higher, but you'll risk stability. If you go lower, then you'll sacrifice performance (or so the manufacturer claims). If you compare the G.Skills to your value RAM, you'll see that the G.Skill has tighter timings, albeit at the cost of more clock cycles. Still, these timings are better because there is more stability than the value RAM.

If the timing wasn't reason enough to make the switch, then consider the energy cost. We're not talking dollars and cents here, rather the cost is the overall performance. As you can tell, higher voltage demands mean more energy is used, and with that extra energy comes extra heat.

WEI isn't necessarily indicative of performance measurement, rather, its greatest purpose is comparing computers. For example, if you were in the market for a new computer, you could compare two (or more) systems by their WEI scores. Although you upgraded your RAM, your WEI didn't change because the score is based off of the lowest scoring component. So, this means either of two things: 1. Your value RAM and G.Skills are considered to be equal, according to Windows; or 2. the RAM wasn't the lowest scoring piece of hardware.

Overclocking RAM is done in either of two ways: BIOS or a GUI-based tool. All motherboards have a BIOS or UEFI where you can change the settings of your hardware. Some motherboards have accompanied software that, when installed, allows users to make changes to their hardware without going into the BIOS. Either way you choose, you need to look for the DRAM settings and select the frequency from a list.

WEI is not an accurate measurement for performance. I have heard of cases where people need to reinstall Windows for WEI to recognize the new hardware correctly. Did you run the WEI test again, and it came up with the same exact score? If you use a memory benchmark test, I can assure you performance is night and day from DDR2 to DDR3.

tRC is fine at 39. If 1T is stable, you can leave it, that is the best performance setting. Some systems require 2T to be fully stable, so it depends from each computer.

Thank you
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