A couple of points of clarification.
I too work with 1080p rather than 4k. Hence my concern with the overkill on gpu.
I don’t find many problems running Premiere Pro on my current high end iMac but I do note delays in heavy work in After Effects and C4D which is what I really need to address with the new machine.
I have my footage on a separate RAID 5 hard drive and my apps on an ssd drive in the IMAC.