iMac Retina 5K 27-inch, Late 2014 - worth upgrading RAM from 16GB to 32GB? | MacRumors Forums
Timetec 32GB KIT(4x8GB) Compatible for Apple DDR3L 1600MHz PC3L-12800 CL11 for iMac (Mid 2011, Late 2012, Late 2013, Late 2014 Retina 5K, Mid 2015 Retina 5K) SODIMM Memory Module MAC RAM Upgrade at Amazon.com
How to upgrade RAM in the (Mid 2017) 5K iMac and save up to ~$900 [Video] - 9to5Mac
iMac with Retina 5K Display 2014/2015 Memory Upgrades
Install memory in an iMac - Apple Support
iMac with Retina display review: best in class, but not everybody needs one | Engadget