imac mid-2017 27" second monitor support

Will a mid-2017 27" imac support a second monitor? I'm a professional photographer currently working with an NEC PA242 monitor that is calibrated with Spectraview II software and xrite i1plus colorimeter. Research shows that imac 5K screens cannot be calibrated sufficiently for photo evaluation. I want to connect my NEC monitor to a new imac and use it for critical image work. On digilloyd.com I read, "An iMac 8K would win me over, since I could run the PA302W as a 2nd display." This implies that the current 5K iMac won't run a second monitor. What is the real story?