I have an iMac 4K and use it mainly for photography. Bought a rMB principally as a substitute for my iPad Air 2 as found the keyboard setup and working with photos remotely to be less than optimal. Love the rMB and am eventually going to sell my iPad. Took a bunch of pictures at a 50th wedding anniversary with my Canon 5D Mark III and sucked them into Apple Photos (former Aperture user). Did simple editing there and employed Photoshop Elements for the first time using clone tools to make some unattractive objects disappear. Found the trackpad to be silky smooth, no lag at all. By blowing up the photo I could easily adjust it on this way smaller screen. Anyway went back to the iMac and Photos crashed. I could see all my new photos made it up to the cloud, which was a relief, but have an unusable Photos app on my main machine. Think I took a lightning hit. Keychain crashed. Lots of problems. Found the rMB to be an able substitute for at least the short term. I don't hook it up to anything, really using it like a souped up iPad. Very happy with it. Not going to get into the keyboard thing as I love it, but know others don't. Just wanted to post that it is fast enough for my photography work (have 45K full resolution pictures in iCloud photo library). Some of my hesitancy to getting this machine was for that work, but find it very capable to perform my mainline work as a salesman with Outlook, Powerpoint etc. In the case of my iMac going south though it was wonderful to have something capable to do very similar things while I figure out how to get it back to normal.