How did you know it was running at 500 or so MHz? Can you give us more information? What specific brand of RAM is that? It's most likely the "base" clock speed of your memory, which you still need to multiply by 2. In my case, my memory is running at 640 Mhz, which means that it's 1280 Mhz (almost 1333, because that's the closest my CPU RAM ratio would allow) effectively.
Use CPU-Z (download at www.cpuid.com) and run the application. Click on the "Memory" Tab, and check what "DRAM Frequency" is saying. Whatever is there, multiply it by 2 to get your effective frequency. In my case, it's showing 642.7 MHz. So my effective DDR3 frequency is 1285.4 MHz.