I've got an early 2008 Mac Pro with 4 Gb of memory which I would like to upgrade, but I'm unsure of the memory speed. In my "About This Mac" dialog it says the memory speed should be 667 MHz, but online (even on Apple's own site), it says 800 MHz. Is it okay to get 800 MHz memory and mix the two, or should I hunt for 667 MHz memory? Or replace my existing 667 MHz memory with 800 MHz?
Best Answer
The difference between 667 and 800 is negligible at best. You will not perceive any difference at all in your daily tasks regardless of what those may be, the one exception being if your job happens to be running theoretical benchmarks all day. You will get a bigger performance boost from populating all 8 slots than you will the performance decrease from having 667 in there. The price premium for 800 makes it a ridiculously poor decision, dollars/performance.