Don't you have crossfire 290's like me? what game is there currently out or even on the horizon that gives a "much better gaming experience" with Mantle on CF 290's?
Not trying to be a tool here, I know Mantle will improve the experience for people with midrange GPU's or weak CPU's, but for those of us with decent setups it's pretty mute. I.E I am looking forward to playing Star Citizen more on my SLI 780 rig more than my CF 290 rig because it will look better on the green rig due to PhysX, granted the game will be playable under Mantle on lower spec systems that wouldn't run it under DX, but still.
I fail to see how our AMD rigs are getting the better deal here. The way I see it my CF 290 rig gets two years of games being just as playable in DX as they are in Mantle, then it gets to play games in DX12. My SLI 780 rig gets two years of being able to play games fine in DX11 while looking better with PhysX (where applicable ofc), then it gets to play games in DX12 and again PhysX where available.
/shrug.