You have no idea what you are writing about in case of Mantle. Mantle is a low-level API that is FUNCTIONAL base of every modern gaming API that exists: DirectX 12, Vulkan, Metal. AMD made it because of the constaints of workforce made to optimize drivers, for games that were coded directly for one specific vendor: Nvidia. A guy from EA to simplify work at code of a game came with an idea of Low-Level API, and went everywhere he could: Nvidia, Intel, IBM, and everybody didn't see the future in it. Everybody, apart from AMD. AMD didn't see the potential in it until they started to experiment with it. And it of it went. Mantle brings functional simplicity to game code, and can be run on every hardware that can operate on each API. AMD put it Open Source, Intel, ARM, Imagination Technologies, Apple(Metal), Nvidia. All of them took it. Apart from one company. Nvidia. Also, Nvidia payed Microsoft to lock some features of DirectX12 only for Nvidia hardware. Features, that are so meaningless, that can be used only for Marketing purposes. Guess that marketing catched you easilly. Like many, many more people.
Why not GTX965M? Because it uses 65W of power ALONE. Also, if Im counting this correctly: M370X should be around GTX950M in terms of performance.
M370X should be around 30W of power draw. So that is efficiency. 30W part is as fast as 45W chip.