Here's a conundrum for you all… I have a 2008 Mac Pro 3,1 2 x 2.8 GHz running El Capitan 10.11.5. I had 16GB of RAM made up of a mixture of 800mhz and 667mhz modules.The presence of the 667mhz causes even the 800mhz modules to run at 667mhz so I decided to purchase 4 x 4GB modules so that I could do away with the 667mhz modules and increase my total memory at the same time. I ran Geekbench tests along the way and I had surprising results… First up is the pre-upgrade test. So 16GB total memory made up of 8 x 2GB modules, and a mixture of 667mhz and 800mhz. Next, we have my 800mhz modules only total of 20GB total, made up of 4 x 4GB and 2 x 2GB. Oddly, more RAM and purely 800mhz yielded a lower score. So, after coming to the conclusion that 667mhz wasn't so bad after all I filled my last remaining slots with 2 x 2GB 667mhz sticks to take me up to 24GB running but running at 667mhz. More RAM but lower than 16GB running at 667mhz. Go figure. Does anyone have the foggiest idea why this could be??