Radeon R7 260x 2GB Dual-fan ID 6658 works fine in yosemite and El capitan with ATI Injection and fake id 0x66401002 but never worked with 2 monitors would have like to add FB patch support for this GPU in the future.
Here my R7 260x Full FPS in Games, QE / CI emulators and everything OK.
But I only have it working 1 Monitor in DVI when I start with 2 monitors it gets everything black screen thanks !!
If you can, can you help?