Am with my iMac 5k of LR 5.7 on the CC 2015 version. To date, a big mistake, especially working with the brush is almost impossible extreme delay between brushwork and display. The problem seems known, according to Adobe (support staff), the problem with the current graphics card driver for MAC OS 10.10.3. I recommended following the nice man: I should me the new MAC OS install 10.10.4 update (is a Beta version), as the graphics card driver with the new Lightroom CC is compatible. Alternatively I could take out even the hook for use in graphics processor or with LR 5.71. work until the new MAC OS 10.10.4 is out. The support for the GPU I had taken out earlier and in fact may notice a marked improvement, a smooth work will not be accepted. With a heavy heart and in good faith I have then the Beta version of MAC OS and installed 10.10.4, to my disappointment, I could not notice any improvement. I wonder as well why Apple needs to make improvements, especially the hardware test, the part of Adobe, a 5k iMac was used and this has impressively well. Ok, so I install my back LR 5.7.1, since everything worked. The absolute low blow hit me unexpectedly, LR 5.7.1 no longer recognizes the converted from LR 6 catalog. I'm curious how it goes on to say Adobe is still pending. Until then, I rate only by a star, and I hope with my review to many i Mac 5k users protect them from a mean disaster.
