I do not own a RX 480, as the original GTA V - RX 480 video belongs to GGPC and can be watched here:
https://www.youtube.com/watch?v=fQ69N...
This is not an apples to apples comparison.
The systems being used are different and GTA's graphical settings are only slightly different.
In the advance graphics options I had to drop the Extended distance scaling to medium because the GTX 970 doesn't have enough VRAM. Other than that, the settings are the same.
GTX 970 video was recorded with external recorder, and I cannot comment on the RX 480 video.