The expensive one usually come with higher factory OC (it means will pull more power as well), and a better cooling system. In my experience so far. Video editing is not that demanding. Yes, it will still put the GPU under stress, but nowhere near those high demanding 3D games. 100% GPU utilisation for video editing is different then 100% on running Furmark. So, almost any mid range after cooling can handle the heat nicely for video editing. The stock reference cooler is already good enough to keep the GPU away from overheat. However, it usually quite noise (if compared to the after market cooler), and unable to fully eliminate GPU thermal throttling.
For better after market cooling. They usually more quiet, and allow the GPU to run just below the thermal throttling temperature (throttling may still occasionally occur under extreme load).
Those expensive one usually can keep the GPU few more degrees cooler than the "cheap" card, which means the GPU can stay at the OC clock speed constantly (no thermal throttling).
Of course, some card build with better material, some manufacture has better QC, some provide longer warranty, some has better customer service, and some card come with more / better accessories. All these can lead to one card significantly more expensive than another one.
IMO, for video editing, the difference is not that huge. If you go for the very best 1080, usually is most cost effective to go for the cheapest 1080Ti.
By considering you are still using the 5770 (that means the 5770 actually OK to get the job done), I will say any 1080 will be fine for you. Just go for the cheapest one (if course, the source need to be reliable if it's a used card).
