I need some help from the team here. A couple of months ago, my Imac 27" I7 died (motherboard) and apparently apple no longer makes the motherboard for it. So I decided to get a Mac Pro, 6 core, 16GIG unit. I am an armature photographer and I send some of my time using Lightroom and Photoshop. Lightroom runs very slow on this computer. e.g Preview changes (\) takes 3-4 seconds Vs less than 1 second on my macbook air. Same goes to applying filters; much faster with the air. I have tried several "speed optimization" suggested found on YouTube (increase cache, disable 3d processing, etc) to no avail. What am I missing?