I got a rx 480 today and I can tell the performance boost in 2.79 with Linux on the latest AMDGPUpro driver, for example Koro scene rendered in just 9 minutes, that's bookers!!! (with 2.78c it took like 40minutes) but I see something pretty strange with RAM usage, with 2.78c the RAM usage goes around 400M but with 2.79 it goes to 2394M, I tried another scene that I know consumes a lot of RAM. Pool deck scene from architecture academy, not part of the benchmark scenes, so with 2.78c the RAM usage was 2662M, but with 2.79 the RAM usage was 4663M, it is if there were a constant overhead in RAM usage. Not sure if it's a bug or this extra 2gb of RAM usage is part of the improvement. For me it doesn't matter much because I have the 8gb version but for others that only have 4gb may be a concern.
Another thing that I like to point out is that I can now see videos while rendering with 2.78c or 2.79, with my last nvidia card, gtx 750ti, I could never do that because the GUI always got laggy no matter how big or small the scene was.
With the 2.79 I notice that ram usage increment too.
"Blender is not free is better than that it's opensource"