Ok, GTX 780 vs R9 290x - Page 4
Poll Results: Which one?
66% (28)GTX 780
33% (14)R9 290x
If all Mantle provides is a performance boost I would expect it to be at least 20%. Look at 3DFX's Glide, games written for it played much better (supposedly) on their GPUs.
That said, I'm also expecting Mantle to boost visuals by massively increasing the number of draw calls the CPU can handle, so we get lots more stuff on screen and everything looks better. Add in TrueAudio (some proper 3D positioning + HRTF ) and I reckon games will be much more immersive on AMD cards - if devs take advantage of these offerings.