You will truly be getting what you are paying for here, but I do feel that you have chosen to leave out a pretty big player on the market. The 290 (Not 290X) is both cheaper and in most cases better than the 780 GTX. I you are contemplating a GPU in that price class then you might aswell take what you will get most bang-for-the-buck with - Which is the R9 290.
When it comes to video editing, all of the rendering you will be doing is CPU based anyway, so really it doesnt matter much about which GPU you will be using for the actual editing, they will perform aprox the same.
So my vote goes on: R9 290.