I have a MacPro5,1 [6-Core Intel Xeon, 3.33 GHz, ATI Radeon HD 5870] that is a workhorse business machine for me. I primarily use it for Illustrator (work) and for Photoshop/Lightroom (photography). I had Mountain Lion running on it forever, and just upgraded to Yosemite. In running the system profiler, I realized that my machine has 4 RAM slots, but only 3 have RAM in them, 8GB each. (I honestly thought I maxed out the ram a while back, and never paid much attention.) I just wanted to know if adding another 8GB of ram to the empty slot will even make any noticeable difference at all. It's about $55 for another 8GB of ram for that slot. Just wondering if anyone has gone through this, or if it's a waste of $$$ as it might be unnoticeable. Any feedback is appreciated, thanks.