So... 2 weeks ago I upgraded to a 5K iMac from my 2011 MacBook Pro which was on its last legs. Everything works great.. except for Lightroom. The preview updates were slow as molasses on a feburary morning, and hitting the Before/After keyboard shortcut took between 5 and 7 seconds each time to see what I had done to an image. Overall the LR experience was miserable. I tried everything under the sun that I've found in these forums. Turn on/off the GPU, optimize and flush everything, move working images to an SSD, build smart previews, build 1 to 1 previews, build smaller previews... etc. I fired up my old, tired 2011 MBP with an 2.4 i7 and 16gigs of ram that has been my workhorse for years. It ran the latest LR CC 2015 about 3 times as fast as my new 27" 4.0 i7, 16gig, 4gb VRAM, 3TB Fusion drive Retina iMac. What was the difference besides the processor setup? Both were running El Capitan, both were running the latest version of Adobe CC. Both were actually using the same catalog I copied over from one machine to the other with the files on external SSD drives. The difference was what others here have said...The Retina screen. So just out of curiosity I changed the display to a non-Retina resolution.... ah hah! This worked for me, so give it a try: In System Preferences --> Display, hold down the Option key while clicking on "Scaled" in the Resolution section. You will see the list of resolution choices. Now down below that box is a checkbox that says "show low resolution modes". I selected 2880 x 1620 (low resolution) mode, which basically kept my resolution but turned off the Retina pixel depth. Yes.. it isn't as beautifully clear as the Retina resolution was.. but for someone like me who is working on batches of files per day in LR and PS, it sped me back up to where the performance should be. So until Adobe figures out how to speed up LR to work with a large Retina display, I'll have to keep my screen set at this depth. Give it a try and let me know if it worked for you!
... View more