Editing what? Program code? Audio? Video? CAD?
Performance scaling in pro apps with high end GPUs depends on many factors. The CPU continues to be the most important component in most workstation environments, with nice GPUs offering performance improvements in limited areas.
Here's an article that may offer some insight: http://www.pugetsystems.com/labs/articles/Adobe-Premiere-Pro-CC-Professional-GPU-Acceleration-502/
Notice that in some cases, increased GPU strength doesn't help (1080P encoding stops scaling above the K2000 on the Z87 platform, which is the workstation equivalent of a GTX650, we don't observe any additional scaling in that workload until we get more CPU involved (X79)).
In terms of performance/$ in many GPGPU workloads, The $100-200 range is the sweet spot for GPUs, with Maxwell GTX750 and GTX750Ti, and R7 260X and R9 270 offering the most usable GPGPU performance/$ when considered overall. Above that level of GPU performance you'll run into more and more CPU bottlenecks that prevent the GPU from assisting any more. This class of GPU will offer most workstations that don't depend on workstation drivers the highest value. For many users, the i7-4930K + GTX750Ti would be a better than an i7-4770K + GTX780. YMMV.