Still on an R290. : DAMD R9 290. Playing BF4 with Mantle was the best experience I have ever had with gaming. 144 fps gaming with no dips. I don't what happened with Mantle since, but I don't think Vulcan can hold a candle to it.
DirectX 12 and glNext (later renamed Vulkan) implemented Mantle features close enough in performance, making Mantle obsolete. Porting Mantle to DX12 was rather easy as well.