I think you will find that the speed of the network and the drives will be the biggest throughput issue, not just the computer and graphics cards per se.
I have worked on numerous 4K projects where we kept everything in 2K all the way up until final delivery. Color correction was all done at 2K, then we swapped out the 2K files for the 4K files, then rendered and delivered 4K. I'm not convinced you actually need to see 4K files during the editing process. For the final screening, sure -- but you need a lot of horsepower (and a capable monitor) to pull that off.