I currently have a 27" mid-2011 iMac with the following specs: Processor: 3.4 GHz i7 Memory: 16GB Graphics: AMD Radeon HD 6970M 1024MB About 2 years ago, I bought a Samsung 840 EVO 500GB Internal SSD with an enclosure, and now I use that as an external SSD via Thunderbolt to run the OS and all applications. The iMac hard drive is used for photo and music storage. I run quite a few programs at a time. I do a lot of web browsing, photo editing (Photoshop, Lightroom, etc), etc. I've been going back and forth debating on whether I should upgrade. Obviously the 5K screen would be the biggest upgrade. Performance wise, would I notice a substantial difference if I upgraded to one of the 2015 27" models?