The 480 is not a bad coice for that rig especially that the pc is not meant for heavy gaming. But if you wanted a little more performance you could also go Nvidia and get the new GTX 1060 which performs just a littlebit better than the 480 or if you wanted outstanding performance for the same ~$250 price point you could also get the GTX 970 which would be a really good pair for your CPU, but keep in mind, that is now a generation behind the latest GPUs from Nvidia. Of course all of the aforesaid GPUs offer very high end performace for editing and I don't think you would regret getting either one of them.

The 480 is not a bad choice for that rig especially that the pc is not meant for heavy gaming. But if you wanted a little more performance you could also go Nvidia and get the new GTX 1060 which performs just a littlebit better than the 480 or if you wanted outstanding performance for the same ~$250 price point you could also get the GTX 970 which would be a really good pair for your CPU, but keep in mind, that is now a generation behind the latest GPUs from Nvidia. Of course all of the aforesaid GPUs offer very high end performace for editing and I don't think you would regret getting either one of them.