Hello I finally bought iMac 2017 3.8GHz quad-core 7th generation Intel Core i5 processor 8GB 2400MHz DDR4 500 GB SSD Radeon Pro 580 with 8GB video memory But Lightroom is working very slowly. Optimization is done, there's nothing you can do about it. Develop tab works very slowly while editing between pictures. It looks like no difference either iMac 27 '2011 and 16 gb ram or iMac 27' 2017 and 8GB. I am waiting for the new 32GB of RAM, totaling 40GB. But as far as I count in forums, it does not even benefit from 128GB. RAW photos are LACIE HDD RAID 2TB Thunderbolt with Adapter to USB 3.1 Lightroom bad ... Sorry for the bad English.