MPG Lloyd tested the 2019 iMac 5K 3.6 GHz Intel Core i9 8-core / 128GB / 2TB / Radeon Vega 48. Purchase with 8GB memory, then add 64GB or 128GB OWC memory. See recommended Macs for photographers and videographers.
These tests made possible by loaner gear from B&H Photo and OWC, so please buy your gear at B&H Photo and OWC/MacSales.com using any link from this site or MacPerformanceGuide.com, ditto for OWC/MacSales.com. See also 2019 iMac 5K: Recommended Models and Accessories.
Unsure which Mac to get or how to configure it? Consult with Lloyd.
In my review of the 2019 iMac 5K I cover a lot of photography-related performance metrics.