Just a month ago, things were different. My iMac 5K (i5 3.5, M290X, 16Gb RAM) was a great computer that did fine. Just fine. I mean, I liked it a lot, the screen was amazing and I never regretted my purchase, but not everything was great. I did find the UI lag a bit annoying. Also, Photoshop CC was a bit problematic on a Mac. I don't really remember when I started noticing it, but Photoshop would sometimes feel sluggish. Especially when moving around groups with lots of layers and lots of layer effects. This did not occur on Windows, even on lower spec computers. Fast forward to today. My iMac is running the DP1 of El Capitan and a brand new Photoshop, CC 2015. Well, first of all, the iMac is really fast on El Capitan. Faster than my i7 MacBook Pro 15" Retina, so I can imagine the horsepower was always there, but Yosemite somehow managed to bring it down. Everything, from UI animations to PDFs is really smooth now and 100% lag free and the computer just feels really fast. Then more good news: the new Photoshop got rid of all the lag, and moving those demanding groups is as fast as it should be. Every other part of the app feels speedy as well. In fact, for the first time in a long while, the Photoshop experience is better on OS X than on a PC. And for me, Photoshop is the single most important program I use. So, I finished work for today and thought - this is the best and fastest computer I've used for Photoshop. And I've used it on faster PCs, i7s with high end Nvidia cards - the iMac 5K feels faster now. Even better, it should be faster (!) when Adobe implements Metal. If any Photoshop user is still considering whether to get the iMac 5K or not, just wanted to share my experiences.