Hello, I have a: Late 2014 27" iMac -4GHZ i7 -32GB 1600 MHz DDR3 -AMD R9 M290X 2048MB -3TB Fusion Drive I made the huge mistake of upgrading to OS Sierra, which is slower than the last OS, which was slower than the one before that. I'm not looking into what my options are for getting my system up and running lightning fast again. I work in Lightroom & Photoshop CC all day and night. My images are stored on an external thunderbolt raid (https://www.amazon.com/Akitio-LYSB0...d=1480552899&sr=1-2&keywords=thunderbolt+raid) That has 4 500GB SSD drives running RAID 1+0. According to BlackMagicDesign disk speed test I am getting inconsistent read/write results. Anywhere from 200MB/s - 985MB/s read, and 100MB/s - 400MB/s write. My question is - where is the weak link in my system? I've been considering going to the 2015 iMac so I could start out with a better video card, internal SSD, & 64GB ram. Or is my RAID system not the best & quickest it could be? I'm open to any suggestions.